As running a mail server brings numerous challenges, you need to analyze every detail with care to reach the right decision for you. The first factor you should bear in mind is the MTA (mail transfer agent): will it be relay-only or full-fledged?
Relay-only (otherwise known as send-only) MTAs are capable of forwarding emails to another server, usually your ISP (Internet service provider’s) SMTP server. Some common relay-only MTAs you might recognize are msmtp, sSMTP, and nullmailer.
This form of MTA is a solid option if you intend to send emails to your address (e.g. Gmail, Outlook). But consider these factors carefully before you commit to a choice:
- Is the MTA capable of queueing emails to be delivered later in the event of a failure?
- Can the MTA meet the requirements for connecting to the ISP SMTP server (such as a certain authentication or TLS)?
- Will the MTA replace the system MDA (mail delivery agent) — if so, it’ll handle all the system’s mail.
Full-fledged MTAs (otherwise known as mail hubs) are designed to handle all details of the Internet mail delivery. This form of MTA gets emails from relay-only MTAs before forwarding them on (examples include Exim, Sendmail, and Postfix).
Give yourself time to think about some important areas to help you find the right option for your goals: specifically, viability, performance, security, and documentation. This list could be more extensive based on your personal goals, and you could go deeper into various technical aspects with these aforementioned areas. For example:
- How minimal and careful the syntax is
- The number of configuration files
- Stability of the code
- What embedded scripting language will be utilized
- The minimum suite of features
- If the source code will be contributed to frequently
- Plus more
Taking a Closer Look: Exim vs Postfix vs Sendmail
While Postfix is an MTA with a clear emphasis on security, Sendmail is standard for Unix systems and Exim can be customized so intricately its flexibility is beyond most MTAs. Here are some more key details to help you make your decision:
|Server OS support||Cross-platform||Cross-platform||Unix-related|
|Auth methods||PLAIN / LOGIN / CRAM-MD5 / DIGEST-MD5 / ANONYMOUS / EXTERNAL / G2 / GSSAPI / GSS-SPNEGO / KERBEROS_V4 / NTLM / OTP / PASSDSS / SCRAM / SRP||PLAIN / LOGIN / CRAM-MD5 / DIGEST-MD5 / ANONYMOUS / EXTERNAL / G2 / GSSAPI / GSS-SPNEGO / KERBEROS_V4 / NTLM / OTP / PASSDSS / SCRAM / SRP / X.509 PKI auth via STARTTLS and EXTERNAL||PLAIN / LOGIN / CRAM-MD5 / DIGEST-MD5 / ANONYMOUS / EXTERNAL / G2 / GSSAPI / GSS-SPNEGO / KERBEROS_V4 / NTLM / OTP / PASSDSS / SCRAM / SRP / SPA / Dovecot SASL / GNU SAS / Heimdal GSSAPI|
|Built-in antispam||Addons||Settings + SpamAssassin||Settings + SpamAssassin|
- Focus on security
- High-quality documentation available
- Compatible with Sendmail
- Queueing operation speed is high
- Active development
- Configuration is simple (parameters to be specified within the config file)
- Customization can be difficult
Postfix offers a wealth of options, features, and parameters, with a security-focused design. While Postfix may be utilized with plenty of mail filters from the start, you’ll still need to figure out how to use them to adjust logic.
- Impressive configuration
- Highly portable
- Considerable flexibility
- Security mechanisms are fairly weak
- Customization can be challenging
It’s fair to say Sendmail could be on its way out. Its market share has dropped significantly since 1996, plugging from 80 percent to 4 percent of all public email servers online in that time.
- Compatible with Sendmail
- Large, highly supportive community
- Support for cPanel
- Nice scalability
- Significantly flexible configuration (as well as declaring variables, Exim allows you to create an email processing script due to having something akin to a scripting language)
- Can be complicated
- Queuing operation speed may be slower than expected
- Architecture is monolithic
Exim is similar to a framework with a unique application language capable of undertaking complicated configurations. The multi-step mail processing logic is advanced enough for even the most complex cases.
Let’s look at Sendmail vs Postfix vs Exim in some critical areas.
What’s the Best MTA for Security?
Postfix has the tightest focus on security of the three MTAs we’re examining. The main reason for this is that its maker, Wietse Zweitze Venema, is a well-known specialist in freeware security.
We can’t label Sendmail as a secure MTA, especially when Postfix was initially conceived as a way to address those weaknesses related to Sendmail.
For most use cases, Exim is pretty secure but still loses out to Postfix. Setting up your Postfix configuration offers better protection against abuse, spam, and exposure of sensitive data.
While it’s difficult to compare with the security offered by Gmail, you face less risk of being affected by a data breach when you choose Postfix.
Which MTA Offers the Best Performance?
Do Sendmail or Exim deliver better performance than Postfix?
Frankly, Sendmail is a weak contender. Exim is utilized for a plethora of high-volume web applications and is capable of handling a huge number of emails every hour. But extensive queues can negatively affect Exim servers’ queue-processing performance.
Postfix has a central queue manager (unlike Exim) and is able to handle queues to a higher standard and a more impressive speed.
Which MTA is the Most Reliable?
Sendmail is recognized as being an inefficient MTA compared to Postfix and Exim. It’s common to see system admins reporting random issues, and they tend to install Postfix or Exim instead.
They’re both drop-in alternatives to Sendmail and nearly equal with regards to reliability. But Postfix stays one step ahead due to its modular architecture: it’s made up of independent system parts that may be switched in the event of a failure. This offers a more reliable user experience.
Which MTA Can be Administered the Easiest?
All three MTAs feature a monolithic configuration file, but Exim offers the most configuration options. While Postfix has a focus on security, it affords an impressive degree of flexibility and simple administration.
That means it’s easier for beginner admins to set up than other MTAs. It actually implements the Sendmail CLI and is compatible with Sendmail mail filters anyway.
Still, Postfix offers less versatility than Exim: the latter has outstanding integration facilities and can provide system administrators what they need. In one form or another, Exim is capable of supporting most of the MTA features. Exim also goes with cPanel, which is one of the most well-known, widely-used control panels available to domain owners.
What’s the Main Reason to Pick Sendmail?
Sadly, Sendmail can’t compete with Postfix or Exim in any area, even usability. There’s no obvious reason to install this MTA, despite it being preinstalled on the majority of commercial Unix operating systems.
Sendmail is also portable, which can be utilized on non-Unix systems (including Windows). This may be a reason to choose it.
Using Plesk with MTAs
Plesk is a highly efficient, well-designed hosting platform that works alongside a mail server, empowering you to run mail services on the same machine you use for hosting websites.
The Postfix mail server and Courier IMAP come installed on Plesk for Linux by default, and MailEnable is on Plesk for Windows. Additional software supported is Dovecot and Qmail on Linux (shipped with Plesk), as well as SmarterMail or IceWarp on Windows (both of which must be installed separately).
It’s not always necessary to restrict yourself to a single MTA. You might find it more convenient and effective to opt for a split setup in which you utilize different MTAs for diverse tasks.
For example: Imagine that you’re not creating the mail server from scratch and running Sendmail already. You’re satisfied with the routing logic, and are happy to increase the performance with Exim, Postfix, or both.
You can utilize Postfix as the initial level of spam- or malware-protection when receiving emails online. You could use Exim for site-specific processing or local delivery of mail. This is just one example — you can make the MTA work for you and hone its architecture to suit your specifications. Just be sure to ask yourself if it’s really what you need or not first.