Cameron Laird's personal notes on mail transfer agents

[I'll be adding plenty more links and comments in spring '99.]

Which mail tranfer agent (MTA) should I use? I generally recommend an underlying Unix host [explain], and there the possibilities include

The Major MIME RFC standards often interest me when thinking about MTAs.

CommuniGate Pro

Nicholas Petreley concludes, "CommuniGate Pro is an elegantly designed e-mail server with features to accommodate installations in environments ranging from a small office to a large ISP." Nick fails, I think, to adequately emphasize CommuniGate Pro's extreme scalability and performance; this is a product that apparently happily handles traffic for a million accounts at a time.



Dave Sill nicely compares qmail, Postfix, and exim in a Usenet posting, to which Erlend Midttun adds several comments. Thanks to Simon Lyall for his help locating the correct links to these two postings.

Among exim's assets are its documentation, generally responsive and courteous (lead?) developer Philip Hazel, and active mailing list. On the other hand, exim is not a particular leader in regard to security.

Several people have told me exim's configuration is "easy", in contrast to that of, say, Zmailer, or qmail.


MD Switch


Netscape Messaging Server

NMS can authenticate against LDAP.


My thanks to Charles Cazabon for the information that
nullmailer is a queuing "dumb" MTA for machines which relay to one or more smarthosts. ... Its design is heavily influenced by qmail, and was created by its author for situations where a "mini-qmail" (queueless "dumb" qmail installation) was insufficient.

It's an excellent solution for workstations in a LAN environment, or for single Unix/Linux machines relaying to an ISP smarthost.

Obtuse smtpd/smtpfwdd



We've profiled Postfix for SunWorld Online and

Correspondents have reported performance as much as three times as great as qmail's. In any case, both qmail and Postfix appear to be much zippier than Sendmail at high volume, although apparently no one has reproduced such results particularly rigorously.



We profiled qmail for the February 1999 LinuxWorld Expo.

While I haven't yet figured out how to backup a qmail configuration (the problem is that qmail works with inodes, so backing up as a file-system isn't effective), Dave Sill assures me that

Queue files are named after their i-node, but they're just normal files. Backing up the queue is easy using any of the standard utilities. The rub is restoring them. Luckily there are a couple utilities that'll munge a restored queue and rename the files properly. Pointers are on (queue-fix, queue-rename).

Bennett Todd describes configuration for qmail, Postfix, and smail in a Usenet posting.

Along with the sites mentioned at [explain], Blue Mountain Arts is a high-volume qmail user [explain].

... Dave Sill ...


Sendmail appears to handle at least two thirds of all Internet e-mail traffic. It's definitely the market leader. It also carries a lot of baggage, as we explain in our profiles of Postfix.

Even old sendmail hands should read Frederick Avolio's review of Sendmail Pro.


SIMS can authenticate against LDAP.


Smail is easy to set up, certainly compared to sendmail, from which it borrows command-line syntax. Some people favor it for its security and configurability. My impression is that it doesn't scale up as well as sendmail. I've spent little time with Smail.

Rumors have come my way that Smail maintenance is moribund. I haven't verified these myself.


The home page speaks for itself:
A secure, effective and simple way of getting mail off a system to your mailhost. No suid-binaries or other dangerous things ...

Warning: the above is all it does. It does not receive mail, expand aliases or manage a queue. . . .

In the same vein, I often script little embedded MTAs with such languages as Tcl, Python, or Perl [explain details].

Sun-Netscape Alliance

Early-summer-1999 rumor has it that The Sun-Netscape Alliance will offer a "melded" update of NMS 4.1 and SIMS 4.0.


Bennett Todd wrote
The first serious attempt I know to bring modern security and performance concepts to bear on the current email environment was Zmailer ...
Correspondents tell me that Zmailer is, in at least some high-volume situations, much the best performing MTA. CommuniGate Pro also makes strong claims about performance; so far, I've tested neither of these. My emotional reaction in regard to the former, at least, is skepticism, just because Zmailer is a monolith like sendmail.

Zmailer's in use at several high-profile sites. It handles Hotmail's inbound traffic.

Zmailer's a setuid monolith.

Cameron Laird's personal notes on mail transfer agents/