QMail: A Better Sendmail? - continued

Efficiency: the Big Draw
Security is essential, but it may not top another reason that admins are drawn to QMail: improved performance and operational efficiency.

Simply put, QMail is fast. Bernstein tested throughput on his relatively puny Pentium 100 running BSD/OS. He found he could easily receive and deliver 200,000 independent local messages per day.

Delivering the same message to many local mailboxes is even faster: Distributing 1,024 copies of the same message took 25.5 seconds, equivalent to 3.4 million deliveries per day. Remote message delivery is bound by DNS and SMTP, not to mention WAN latency, but sites moving to QMail have been found to sustain previous SendMail volumes on smaller machines.

QMail can also use NFS to deliver and retrieve messages reliably. Fast, lightweight code that uses distributed storage is an attractive combo. According the Carey, "QMail solves delivery problems: It allows me to safely use inexpensive boxes as mail servers, and invest infrastructure dollars elsewhere"—for example, storage area networks, and greater WAN bandwidth.

But Carey admits that he hasn't yet stressed QMail and cannot vouch for its stability under heavy load. NetReach's QMail server is supporting a dozen virtual domains, but Sendmail is still supporting the bulk of subscriber mail traffic on other servers. On the other hand, QMail isn't untested: 30 million Hotmail users have been sending outgoing messages with QMail since 1997.

Customer-managed virtual domains also bring greater operational efficiency. QMail virtual domains allow mail destined for many customer domains to be received by a single server, then efficiently filtered into user@domain mailboxes—with QMail, it isn't necessary to alias each user to a local domain mailbox (e.g., map lisa@corecom.com into lisap@netreach.net).

Moreover, QMailAdmin allows each customer to manage his own domain, adding or deleting users, defining aliases and forwards. "Why do I care how many POP accounts my customers have?" says Carey. "I can set limits and quotas, then charge for storage, and offload user administration from my support staff."

Speaking as a virtual domain customer, I see this as a huge win-win proposition. If I need to change a password, create an alias, or delete a mailbox, I can do it myself in less than five minutes. We're using our mail service more effectively and spending zero time calling NetReach for mail support. Others NetReach QMail users agree, according to Carey. "They love it."

So what are the drawbacks?
The purpose of a trial is to identify both advantages and limitations of a new solution. So it should come as no surprise that QMail brings with it a few drawbacks.

Upgrade blues  QMail is open source. While you can't beat the purchase price (free!), the source changes frequently as the large community using QMail identifies problems, creates patches, proposes new features, and develops add-ons. "Qmail itself compiled fine the first time, but some friend modules are still wet behind the ears," says Carey.

When upgrading to a new version of vpopmail or SqWebMail, Carey often bumps into new compile-time problems. "The problems aren't major. I can usually fix the source. But I'm a sys admin, not a C programmer. I don't have time to help refine the source."

Support logistics  All ISPs are familiar with the need to move forward without loss of productivity, and the delicate balance this requires when deploying open source solutions in a production network. There are several companies that provide commercial installation and support for QMail, among them SqWebMail creator inter7. Carey suggests that professional support is particularly useful for "small ISPs who don't have in-house expertise they can turn loose on QMail, but who can offset up-front investment by using lower-cost mail servers."

Feature growth   While there are a few features Carey would like to see added to QMail, he's been generally pleased with its run-time capabilities, performance, and stability. At the SMTP level, Carey would like to see customer-controlled spam filtering. In QMailAdmin, Carey would like to see a root account with the ability to manage all virtual domains. (Overall virtual domain and mailbox admin requires scripting now.)

On the front end, Carey would add an Address Book to SqWebMail. Carey and I differ in our overall impressions of SqWebMail: he uses it routinely every day, and loves the ability to view all message headers before selectively downloading message bodies (a la IMAP). I prefer composing my messages and replies with Eudora; at work, download time is rarely an issue. I thus depend on SqWebMail only when away from my desktop or laptop. In that environment, I'd dearly love to see my login/password, if not all message exchanges, encrypted with SSL. Carey also disables user-level password change because allowing SqWebMail and POP mail passwords to differ is undesirable.

Phased deployment
Carey would like to deploy QMail more widely, with phased rollout. Outbound mail can be transitioned to QMail transparently. For inbound mail, existing customers can continue to access QMail with POP clients, but virtual domains require one user-visible configuration change: instead of checking mail for user "lisa," I must now check mail for "lisa@corecom.com". Thus, moving to QMail involves commitment, says Carey. "Once you tell a customer to change user settings, you absolutely don't want to tell them to change back."

To minimize impact, Carey would bring up all new virtual domain accounts on QMail first. He'd then selectively move high-maintenance accounts over to QMail, using the lure of self-administration to sell customers on the one-time switch. Finally, he'd transition legacy accounts after QMail was running well under stress for considerable time.

For more information about QMail, visit the QMail Home Page site or Bernstein's QMail page at ftp://koobera.math.uic.edu/www/qmail.html. For information SqWebMail or inter7, visit http://www.inter7.com/qmail. To try SqWebMail for yourself, visit the demo at http://webmail.inter7.com and login as user webmail, password webmail (only one user can login to the demo at a time).

Also see the Linux Planet comparison between Sendmail and Qmail.

 —End

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