Author: RunCloud Team

In this post, we’re going to take a look at a vital part of the email system, called the Mail Transfer Agent, sometimes referred to as “mail delivery agent” or even “mail transport agent“. We will discuss what the mail transfer agent is, the advantages of using the mail transfer agent, and finally take a look at some of the best transfer agents for Linux servers.

Did you know that email has been around since 1971, and that currently there are over 8 billion email addresses in the world, used by over 4.5 billion users?

Also, every single second sees over 3.13 million emails sent, which means that since you started reading this article, roughly 8 million emails have landed in people’s inboxes. At least a few of which were actually wanted!

Let’s get started!

What is a Mail Transfer Agent?

An MTA, or Mail Transfer Agent, is a crucial component of the email delivery system that is responsible for transferring emails between the computers of a sender and a recipient. It acts as an intermediary, ensuring that emails reach their intended destinations.

MTA Functions

Acceptance

MTAs are like the receptionists for emails – when you send an email from your Mail User Agent (MUA) such as Gmail or Outlook, the MTA is the first to greet it. It checks if the email is properly formatted, and if the sender and recipient addresses are valid. If everything looks good, the MTA accepts the email and lets it in.

Routing

Once the message is received, MTA directs it to the recipient’s inbox. It looks up the MX records to find out which mail server (destination) the email should go to.

Auto-Responses

If an email fails to reach its destination (maybe the recipient’s server is down), the MTA sends an automatic reply (like saying, “Oops, something went wrong!”) back to the sender.

Queueing

If an email can’t be delivered right away (maybe the recipient’s server is busy), the MTA keeps trying until it successfully delivers the message.

Suggested read: How to Send Email from PHP (With Guided Walkthrough)

Best Linux Mail Transfer Agents (MTAs) You Should Try

When it comes to managing email delivery, choosing the right Linux Mail Transfer Agent (MTA) is crucial. Here are some top-performing MTAs that you should consider, along with their key features:

1. Exim Internet Mailer

Exim is a message transfer agent (MTA) developed at the University of Cambridge for Unix systems connected to the Internet. It operates under the GNU General Public License and offers extensive facilities for checking incoming email.

Although the website looks quite outdated, it is still being actively developed, and you can get the latest updates from its GitHub repository.

It provides a web-based administration and configuration tool for easy management which can be configured as an intermediate mail relay, a mail server for multiple domains, or anything in between.

Exim’s architecture allows for complex configurations and customization as most Linux distributions come with sane default configurations for Exim, making it straightforward to set up.

In addition to supporting basic features such as IMAP server, webmail server, and mail filtering technologies, it also provides the ability to automatically process bounced emails or send emails as faxes.

Suggested read: How to Change/Reset MySQL Root Password on Ubuntu Linux

2. Postfix

Postfix is an email agent designed for Unix systems that aims to be fast, easy to administer, and secure. While its external appearance may resemble Sendmail, its internal architecture is fundamentally different.

Postfix runs on various UNIX platforms, including AIX, BSD, HP-UX, LINUX, MacOS X, Solaris, and Tru64 UNIX. It relies on ANSI C, a POSIX.1 library, and BSD sockets.

While configuring Postfix can be challenging for first time users, its security features and flexibility make it worth exploring. Some of its key features include SMTP client support, configurable DNS filters, and compatibility with various databases (e.g., MongoDB, MySQL, PostgreSQL).

Suggested read: Mastering the Echo Command in Linux (with Practical Examples)

3. Proofpoint

Sendmail, a descendant of the original delivermail program by Eric Allman, is a well-known project within the free and open-source software and Unix communities. It used to be an independent project of its own, but now it is a part of the email protection and thread intelligence suite in Proofpoint.

Sendmail provides a general-purpose email routing facility, and offers a versatile set of delivery methods for sending emails that makes it suitable for large, complex environments.

Sendmail prioritizes security, and its open-source nature allows for community scrutiny and contributions. Additionally, the software releases are signed with PGP keys – which means you can be sure that you’re not running a modified version of the software. It also enables enterprises to plan their messaging infrastructure for the long term, including virtualization, consolidation, and cloud migration.

Suggested read: Using Mailgun To Send Transactional Email From WordPress

4. Axigen

Axigen is an all-in-one email, calendaring, and collaboration platform designed for demanding users, from small businesses to large service providers. The free mail server license includes unrestricted access to new version upgrades, patches, and updates, but technical support is available only for those with commercial versions.

It allows you to gather all your email in one place by retrieving messages from external accounts (e.g., Yahoo! Mail, Gmail) directly into your Axigen inbox. You can also generate temporary email addresses for newsletter subscriptions, or automate administration tasks using the Command Line Interface (CLI) and dedicated APIs.

Team users can grant permissions to other team members to send emails in your name, or define group workflows via public folders – which makes it useful when one colleague is out on a vacation.

Suggested read: How To Speed Up DNS Propagation – The Ultimate Guide

5. Postal

Postal is a comprehensive and fully featured mail delivery platform designed for websites and web servers. It’s open source, and allows you to host your mail server in-house, and configure it as you like.

You can use it to manage mail servers and view mail logs using its easy-to-use web interface, or set up webhooks to receive real-time notifications about message delivery or issues. It supports IP Pools that allow you to send mail from different IP addresses to maintain a good IP reputation.

It also provides a development mode that allows you to automatically hold messages in Postal during testing and development. This is useful if you don’t want to accidentally send out emails to all your customers.

Suggested read: How To Flush DNS Cache — A Full Guide

6. OpenSMTPD

OpenSMTPD is a server-side SMTP protocol implementation, which follows the standards defined by RFC 5321. It enables ordinary machines to exchange emails with other systems using the SMTP protocol. While it lacks frills and is not beginner-friendly, OpenSMTPD offers a fairly complete SMTP solution that is freely usable and reusable under the ISC license.

Despite its somewhat outdated website, OpenSMTPD is actively maintained on its GitHub repository, and unlike feature-heavy alternatives, OpenSMTPD provides a barebones and efficient implementation of a mail transport agent.

Suggested read: How to Copy Files in Linux and Overwrite Without Confirmation

7. Citadel

Citadel is an advanced, multi-user, client/server messaging solution designed for email, collaboration, message boards, content management, and other groupware applications. Whether you’re a small organization or a large-scale public access system, Citadel offers powerful features while remaining easy to install and use.

It is an open-source messaging platform that combines email, collaboration, groupware, and content management. In addition to mailing capabilities, Citadel users can take advantage of a unique “rooms” architecture, bulletin boards (forums), instant messaging, RSS aggregation, and more. You can learn about the additional features offered by Citadel by exploring their documentation.

8. Courier Mail Server

The Courier Mail Server is an integrated mail/groupware server that provides a comprehensive suite of services based on open commodity protocols, including ESMTP, IMAP, POP3, LDAP, SSL, and HTTP. It also offers features such as web-based calendaring, mailing lists, and efficient mail storage using the maildir format.

The Courier mail server can function either as an intermediate mail relay, or perform final delivery to mailboxes. It supports authentication via PAM, LDAP, PostgreSQL, or MySQL, and includes features such as DNS-based blacklists, message filtering, and secure mail delivery channels.

You can use its aggregator proxy which distributes mailboxes across multiple servers, and connects clients to the right server based on the mailbox being accessed.

Wrapping Up

In this post, we have covered different Linux Mail Transfer Agents (MTAs) and how they handle the routing, forwarding, and delivery of emails across networks. We have explored both open source and proprietary tools available for processing emails on a Linux server.

If you are interested in deploying websites as well, then you should definitely check out RunCloud – an all-in-one website management platform.

RunCloud simplifies server management, making it easy for developers, designers, and businesses to deploy websites on the internet. With features such as automated backups, SSL certificate management, and seamless scaling, RunCloud streamlines the process, allowing you to focus on your content and applications.

Ready to take control of your web hosting? Sign up for RunCloud today and experience hassle-free server management! 🚀🌐

FAQs on Mail Transfer Agents (MTAs)

PHP and SQL are two of the most commonly used tools in web development. PHP is a server-side scripting language that is used to create dynamic web pages, while SQL is a database management system that is used to store and retrieve data.

You don’t need to be a Linux expert to manage your servers anymore.

In this article, we will show you how to connect a MySQL database to PHP using the RunCloud dashboard.

We will also discuss two main ways to connect PHP to MariaDB: using mysql_connect and PDO.

Step 1: Create a Database

Before we can start using a database, we need to create a database on the server. We also need to create a user account with permissions to access this database. This can be done easily from the RunCloud dashboard itself.

Open the server on which you want to deploy your application, and click on the “Databases” button in the left menu.

On the next screen, click on “Database Users” and then select “Add New Database User” to create a new user account.

On the next screen, give a descriptive name to the user account and set a password. Be sure to note down these credentials as they will be needed later. Once you have provided the username and password, click “Save” to create the user.

Next, we need to create a database. Click on the “Databases” tab to view all the available databases. To create a fresh database, click on “Add New Database”.

When creating a database you will be asked to provide a name – this can be anything you like. For database collations, you can either leave it blank or refer to our documentation post: Understanding Database Collations.

Finally, from the drop-down menu, select the user account that we created earlier.

Once you have configured these settings, click on “Save”.

Step 2: Connecting to Web Applications

You must deploy a web application on the RunCloud server to run your PHP code. The process to create an application is very simple. In this tutorial we will be creating an empty web application, but the process is similar for any other type of application.

Firstly, go to your web application settings page in the RunCloud dashboard, and scroll down until you see the linked databases section.

Click on the drop-down button, select the database that we just created, and then save the changes.

Next, we will create a PHP file on your server that will host the code to connect to your database.

To do this, click on the File Manager tab in the left menu. Here you will see a list of all the files present in your application.

Click on New > File to create an empty file, and then give it the desired name.

Once you have created the file, click on it. This will open the text editor in a new window where you can edit the file.

Step 3: Coding Database Connection Module

The final step for using a database in your web application is to configure a pre-built library. This will allow you to perform database operations without needing to understand how the database handles these operations. There are two popular ways to do this:

Step 3.1: Use MySQLi

The mysqli connect is a PHP extension used to connect to MySQL databases. It is a simple and easy-to-use method that is ideal for small projects. It is also faster than PDO because it is a native PHP extension. However, it does not support all of the features of PDO.

To use this module, paste the following code snippet in the text editor. Make sure to replace the values of database, username, and password variables with the credentials that you noted down earlier.

<?php
$servername = "127.0.0.1";
$database = "my_app_dv";
$username = "my_db_user";
$password = ".GA8sn,tsP=?5Uy7Lqu#iBy:AzVs3KJE";
// Create connection
$conn = mysqli_connect($servername, $username, $password, $database);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
echo "Connected successfully";
mysqli_close($conn);
?>

Step 3.2: Use PDO

PDO is a PHP extension that provides a data-access abstraction layer. PDO also supports multiple database drivers, which makes it more flexible than mysqli connect. However, it is slower than mysqli connect because it is not a native PHP extension.

To use this method, copy the following code example and paste it into your text editor. Don’t forget to update the credentials in the first three lines with the values that you noted down earlier.

<?php
$database = "my_app_dv";
$username = "my_db_user";
$password = ".GA8sn,tsP=?5Uy7Lqu#iBy:AzVs3KJE";
$dsn = "mysql:host=127.0.0.1;dbname=$database;charset=utf8mb4";
$options = [
    PDO::ATTR_EMULATE_PREPARES => false, // Disable emulation mode for "real" prepared statements
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION, // Disable errors in the form of exceptions
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC, // Make the default fetch be an associative array
];
try {
    $pdo = new PDO($dsn, $username, $password, $options);
    echo "Connected Successfully";
} catch (Exception $e) {
    error_log($e->getMessage());
    exit("Something bad happened");
}
?>

Step 4: Save and Test Connection

Once you have added the code to your server, click on “Save” to save the changes, and then visit the page in your browser. When you request this page, the server will execute the PHP code and establish a connection to the server.

The exact path of this page will vary depending on what you named the file. For instance, if the domain name of your website is https://www.example.com and you named your file sql.php then you can browse this file at https://www.example.com/sql.php.

If you see a “Connected Successfully” message then it means your code has successfully established a connection with your database, and you can now start using it in your code.

Wrapping Up

In this article, we have seen how to connect a MySQL database to PHP. We have outlined the steps needed for creating a database and granting permissions to user accounts before connecting to the database. We discussed two main ways to connect PHP to MariaDB: using mysqli connect and using PDO – both methods have their own benefits and drawbacks.

If you want to host your web application on the cloud, but aren’t sure where to start, then you should check out RunCloud.

RunCloud is a great platform for managing your servers, even if you are not a Linux expert.

With RunCloud, you can easily create web applications, manage databases, and connect PHP to MariaDB. So, what are you waiting for?

Sign up for RunCloud today and take your server management skills to the next level!

When it comes to monitoring system resources on Linux, htop has been the go-to tool for many administrators and developers alike. Its simple interface and real-time metrics have made it a staple in the toolkit of those who prefer a comprehensive overview of their system’s performance.

You might already know about htop, a great tool for monitoring resource usage on your computer, but it is not the only one out there. In this post, we will show you the best 9 htop alternatives for Linux (including Ubuntu and CentOS), Mac and Windows in 2024.

Let’s get started!

What is htop?

htop is an interactive system-monitoring tool for Unix systems, including Linux. It provides real-time insights into system performance, allowing users to view and manage system processes more efficiently than with the traditional top command. htop displays system metrics such as CPU, memory, swap usage, and process information in a user-friendly, color-coded interface. Users can interact with the tool to perform tasks such as killing processes, renicing tasks, and sorting processes by various criteria.

Unlike the standard top command, htop offers a more dynamic and user-friendly experience. It supports vertical and horizontal scrolling, making it easier to view all processes running on the system, and includes features such as searching for processes, tree view for process hierarchy, and customizable display options. htop is highly customizable and can be configured to suit individual preferences and needs.

Suggested read: How to Copy Files in Linux and Overwrite without Confirmation

3 Best htop Alternatives for Linux

While htop is a powerful tool, there are several alternatives that provide additional features and cater to different use cases. Here are three of the best htop alternatives for Linux:

Glance

Glance is a cross-platform monitoring tool that provides a unified view of system metrics. It is designed to be simple yet comprehensive, displaying essential information about CPU, memory, disk I/O, network interfaces, and processes. Glance is easy to use and provides a web-based interface for remote monitoring.

How to Install Glance

To install Glance, follow these steps:

1. Install Glance: You can use the apt package manager to install Glance on your Linux computer by using the following command:

sudo apt install glances

2. Run Glance: After installing the glance, you can start it by executing the following command:

   glances

In the above example, we can see how the Glances displays an overview of the system resources in the terminal over an SSH connection.

3. Web Interface (Optional): If you want to access the same information over a web interface, then you can start the Glance with the -w parameter, this will start a web server where you can see your resource usage.

   glances -w

In the above example, we can see that the server was started on localhost but if you are using a VPS then you will need to configure your firewall settings to view this interface. Fortunately, this is very simple using the RunCloud dashboard. Just go to the Security tab of your server and add a new rule to open your desired port.

In the above example, the Glances daemon was running on port 61208, once you have configured your firewall, you can access the same dashboard in your web browser by entering the IP address of your server followed by : symbol and the port number as shown below.

Suggested read: Mastering the Echo Command in Linux (with Practical Examples)

atop

atop is an advanced system and process monitor that provides detailed information about system resources. It is particularly useful for performance analysis and troubleshooting as it logs system activity and can show resource usage by individual processes over time. On Ubuntu, you can install and run atop with the following command:

sudo apt-get install atop
sudo atop

In the above example, we can see the system metrics and resource usage on the server using atop dashboard. To enable logging, you can configure atop to run as a daemon by editing the configuration file located at /etc/default/atop and set LOGINTERVAL to a desired value (e.g., 600 for 10-minute intervals).

Suggested read: What are Linux Logs? What Are They & How To Use Them

nmon

nmon (Nigel’s Monitor) is a system performance monitoring tool originally developed for AIX and later ported to Linux. It provides a comprehensive overview of system performance, including CPU, memory, disk I/O, network, and filesystem statistics. nmon is known for its lightweight design and efficiency, making it suitable for real-time monitoring and historical performance analysis.

To install nmon, first make sure that your package manager list is up to date, after that you can execute the following commands to download an run it:

sudo apt-get install nmon
nmon

Once running, you can use various keyboard shortcuts to view different metrics. For example, press c to view CPU usage, m for memory usage, and d for disk statistics.

These alternatives to htop offer a range of features that can be tailored to specific monitoring needs, providing powerful tools for system administrators and users alike.

Suggested read: How to Create and Manage Cron Jobs on Linux

3 Best htop Alternatives for Mac

Mac users often require robust system monitoring tools to keep track of their system’s performance and resources. While htop is a popular choice, several other tools offer similar and additional functionalities tailored to macOS. Here are three of the best htop alternatives for Mac:

iStat Menus

iStat Menus is a comprehensive system monitoring tool that integrates seamlessly with macOS. It provides real-time data on CPU usage, memory, disks, network activity, and other system metrics directly from the menu bar. iStat Menus is highly customizable, allowing users to choose which information to display and how to display it.

How to Install iStat Menus

1. Download: Visit the official iStat Menus website iStat Menus and download the latest version.
2. Install: Open the downloaded .dmg file and drag the iStat Menus icon to your Applications folder.
3. Launch: Open iStat Menus from your Applications folder and follow the setup instructions.
4. Customize: Configure the tool to display the metrics you need from the menu bar.

Activity Monitor

Activity Monitor is the built-in macOS application that provides detailed information about the processes running on your Mac, as well as overall system resource usage. It offers insights into CPU, memory, energy, disk, and network usage, making it a powerful tool for everyday system monitoring.

How to Access Activity Monitor

1. Open Finder: Click on the Finder icon in your dock.
2. Navigate to Applications: Go to the Applications folder and then the Utilities folder.
3. Launch Activity Monitor: Double-click on Activity Monitor to open it.
4. Usage: Use the tabs to monitor CPU, memory, energy, disk, and network activity.

mactop

Latest Apple laptops use Apple silicone which was built using Arm architecture, this means that a lot of the software built for x86 chips is not compatible with latest Apple laptops. mactop is one of the few softwares which was specially built for Apple silicone and it is guaranteed to work with all the M1, M2, and M3 series chips.

You can download and compile the source code from its GitHub repository or simply download and install a pre-built binary directly using brew by using the following command:

brew install mactop

Once it is installed, you can start using it via the following command:

sudo mactop

3 Best htop Equivalent Alternatives for Windows

Windows users looking for powerful system monitoring tools similar to htop on Unix systems have several good options available. These tools provide detailed insights into system performance, process management, and resource usage, making them indispensable for advanced users and system administrators. Here are three of the best htop equivalent alternatives for Windows:

Sysinternals Suite

Sysinternals Suite is a collection of tools from Microsoft which provides detailed information about the processes running on your system, including the handles and DLLs that processes have opened or loaded. It offers a comprehensive overview of system activity, making it an essential tool for troubleshooting and performance monitoring.

How to Install Process Explorer

1. Download Sysinternals Suite: You can either visit the Sysinternals Suite page to download the entire suite or manually download individual tools from SysInternals Live website.
2. Extract the Files: After downloading the file, you can extract the downloaded ZIP file to a desired location.
3. Launch Process Explorer: Navigate to the extracted folder and double-click on procexp.exe to launch Process Explorer. This will open a new window where you can explore different processes running on your computer.

4. Launch Process Monitor: In addition to process explorer, you can also launch the procmon.exe file to run the Process Monitoring tool. Once you have opened the tool, you can browse and manage different processes running on your system and forcefully terminate them if necessary.

Suggested read: How To Check Disk Space in Linux

Windows Task Manager

Windows Task Manager is a built-in system monitoring tool that provides real-time information on CPU, memory, disk, and network usage, as well as detailed process management. It is a powerful utility for basic and intermediate system monitoring and troubleshooting which can be used by anyone without needing to install any additional software.

How to Access Windows Task Manager

1. Open Task Manager: On your Windows computer, press Ctrl + Shift + Esc or right-click on the taskbar and select “Task Manager”.
2. View Processes: In the “Processes” tab, view the list of running applications and background processes along with their CPU, memory, disk, and network usage.

3. Performance Tab: Click on the “Performance” tab to see an overview of system resources such as GPU, CPU, Memory, Network, and Disk.

4. Details and Services: If you want granular control over services, then you switch to the “Details” and “Services” tabs for more advanced process management and service control.

btop++

btop++ is an advanced system resource monitor that works on Windows, providing a detailed and visually appealing interface similar to htop. It offers insights into CPU, memory, disk I/O, and network usage, making it a versatile tool for system performance monitoring.

How to Install btop++

1. Download: Visit the btop++ GitHub repository (also available for Linux) and download the latest release for Windows.
2. Extract the Files: Extract the downloaded ZIP file to a desired location.
3. Install Required Dependencies: Ensure you have Microsoft Visual C++ Redistributable installed, if not, download and install it from the official Microsoft website.
4. Launch btop++: Navigate to the extracted folder and double-click on btop.exe to launch btop++.
5. Usage: After installing it, you can use the interface to monitor system performance metrics and manage processes.

Wrapping Up

Monitoring system performance is crucial for maintaining optimal functionality and troubleshooting potential issues on your Windows, Mac, or Linux systems. While hTop is known to users for its comprehensive and interactive interface, there are powerful alternatives available across different platforms.

Recently, RunCloud has announced the addition of RunCloud Monitoring, a powerful tool designed to identify high resource usage and slow SQL queries on your server. This feature helps ensure that your servers are running smoothly and efficiently, saving you time and reducing the potential for downtime.

Whether you are managing a server or using a personal computer, having the right monitoring tools at your disposal is essential. Sign up for RunCloud today and take advantage of our comprehensive server management and monitoring solutions to keep your systems in top shape.