| Lesson 4 | Linux MTAs and MDAs |
| Objective | Describe the purpose of Linux MTAs and MDAs. |
Linux MTAs and MDAs used in Red Hat Linux
Red Hat Linux, including derivatives like Fedora and CentOS, still utilizes Mail Transfer Agents (MTAs) and Mail Delivery Agents (MDAs) for email communication. Here's a brief overview:
Both MTAs and MDAs play crucial roles in the email ecosystem on Red Hat systems:
Even with the shift towards cloud-based email solutions, traditional email setups using MTAs and MDAs are still relevant for on-premises solutions or in environments where control over email routing and delivery is required. If you're setting up or managing a Red Hat system for email, you'll likely encounter or need to configure one of these agents.
Linux has several common MTAs (Mail Transfer Agents) and MDAs (Mail Delivery Agents), described in the following table:
- MTAs (Mail Transfer Agents):
- Common MTAs on Red Hat systems include:
- Postfix: Often the default choice in recent Red Hat distributions due to its security and ease of configuration.
- Sendmail: Historically prevalent but less common in newer setups.
- Exim: Used in some environments for its flexibility.
- MDAs (Mail Delivery Agents):
- MDAs handle the final delivery of email to local mailboxes. Examples include:
- Procmail: For sorting and delivering mail to user mailboxes or further processing rules.
- Dovecot: Often used for its IMAP and POP3 capabilities but also includes LDA (Local Delivery Agent) functionality.
Both MTAs and MDAs play crucial roles in the email ecosystem on Red Hat systems:
- MTAs manage the routing of email between servers, whether sending it to another server or receiving from one.
- MDAs focus on the local delivery, ensuring emails end up in the correct user's mailbox or are processed according to local rules.
Even with the shift towards cloud-based email solutions, traditional email setups using MTAs and MDAs are still relevant for on-premises solutions or in environments where control over email routing and delivery is required. If you're setting up or managing a Red Hat system for email, you'll likely encounter or need to configure one of these agents.
| Program | Classification | Description |
|---|---|---|
fetchmail | MTA | fetchmail transfers email from remote POP and IMAP servers to your local SMTP server.
You will need fetchmail if, for example, you need to retrieve remote email, but cannot use your machine as an email exchanger. |
sendmail | MTA and MDA | sendmail, which delivers most of the Internet's mail, operates as both an MTA and a MDA. It sends email to and receives email from Internet hosts, and it delivers mail to domain mail handlers. |
procmail | MDA | procmail is a powerful MDA that provides extremely sophisticated support for delivering mail. It allows email to be filtered and tagged before delivery, optionally filing mail into content-specific mail folders. |
Selecting Mail and Printing Alternatives
Beginning with Red Hat Linux 7.3, which was the first version to offer the alternatives feature,
two major services were configured to use alternatives: mail transport and printing services.
The alternatives facility let system administrators choose the following, related to mail transport and printing:
As an administrator, you still need to configure each alternative service to work. LPRng is no longer delivered with Fedora or RHEL, although it is still available from sites such as http://rpmfind.net/linux/RPM/. Likewise, the feature for switching the printing service described below is not included with Fedora or RHEL, but can still be found in earlier Red Hat Linux systems.)
In terms of setting up the alternatives side of mail services, much of the work of creating links so that the services can be chosen has already been done. Links relating to the default services are set up in the /etc/alternatives directory. Definitions that identify the alternative components of sendmail, exim, and postfix mail servers are contained in the /var/lib/alternatives directory.
Because much of the configuration has been done in advance, the first step in switching between the different mail services installed on your computer is only a couple of clicks away. The next lesson compares several different Linux MUAs.
- Mail Transport Agent (MTA) : If the sendmail, exim and postfix mail transport agents are installed, as an administrator you can choose which of those services is the default for sending and receiving e-mail.
- Printing: If both LPRng and CUPS printing services are installed, you can choose which service is the default for printing documents.
As an administrator, you still need to configure each alternative service to work. LPRng is no longer delivered with Fedora or RHEL, although it is still available from sites such as http://rpmfind.net/linux/RPM/. Likewise, the feature for switching the printing service described below is not included with Fedora or RHEL, but can still be found in earlier Red Hat Linux systems.)
In terms of setting up the alternatives side of mail services, much of the work of creating links so that the services can be chosen has already been done. Links relating to the default services are set up in the /etc/alternatives directory. Definitions that identify the alternative components of sendmail, exim, and postfix mail servers are contained in the /var/lib/alternatives directory.
Because much of the configuration has been done in advance, the first step in switching between the different mail services installed on your computer is only a couple of clicks away. The next lesson compares several different Linux MUAs.