Sendmail vs. Qmail: A Rational Comparison - page 2
Delivering the MailSendmail has the commercial support of sendmail.com (the company founded by sendmail developer Allman), which also makes the free version available at www.sendmail.org. The commercial version includes better documentation and additional configuration tools that streamline setup and management. Sendmail.com also has a number of other products, such as secure mail switches and versions for non-UNIX platforms. Fee-based tech support is also available.
There are also several consulting groups that provide sendmail support for a fee. Sendmail has an extensive informal support structure throughout the Internet, with web sites and mailing lists being maintained by individuals and groups using it. The answer to almost any sendmail question is out on the Net if you can find it.
Sendmail is only an MTA. It will accept incoming mail via SMTP and it can send outgoing mail using the same protocol. Sendmail requires third-party mail-delivery agents (MDA) like procmail to deliver local mail to local mail directories. Mail user agents (MUA) like the mail application are needed by a user to send and receive mail. These applications are normally used to create and view mail as well. The basic sendmail model applications access mail queues directly from disk.
Sendmail requires other components to provide remote mail pickup using POP3 or IMAP protocols. In this case, it must be complemented with additional applications like imapd. It works with a variety of other applications as well. Qpopper can pick up mail using POP3 and deliver it to sendmail, and is useful where incoming mail will be picked up via Qpopper instead of being sent via SMTP. Qpopper is often used, e.g., on dial-up mail servers. Fetchmail is another popular mail delivery tool.
Sendmail also works with tools like majordomo, the quintessential mailing list manager. There are even management and monitoring tools like the web-based SWAT (Sendmail web administration tool) by Michael Hasenstein. SWAT, similar to the SWAT used with Samba, could use some security improvements but can make an administrator's job easier when setting up sendmail.
This plethora of options is one of the reasons for sendmail's popularity. It can also be rather confusing, as getting the right versions for all the components can get daunting for complex environments.
Qmail, on the other hand, incorporates more into the core system so administrators will not have to go looking for so many components. For example, the qmail-pop3d daemon that comes with qmail provides POP3 client access. Local mail delivery is handled by qmail-local. Qmail can be used with many applications normally designed for sendmail like qpopper, but often their configuration information is tilted towards sendmail.