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Features and Details of Qmail MTA

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Qmail is a mail transfer agent (MTA) supported on Unix. It was written, in December 1995, by Daniel J. Bernstein as a more secure replacement for the popular Sendmail program. Originally an open-source software, Qmail’s source code was later dedicated in the public domain by the author.

Specialties of Qmail

Solid: Qmail’s straight-paper-way reasoning ensures that a message, once acknowledged into the framework, will never be lost. Qmail underpins maildir, another, super-solid client post box design. Maildirs, not at all like mbox documents and mh envelopes, won’t be tainted if the framework crashes amid conveyance. Not only can a client securely read his mail over NFS, any number of NFS customers can convey mail to him in the meantime.

Straightforward: Qmail is smaller than other Web MTA. A few reasons why: (1) Different MTAs have separate sending, associating, and mailing list components. Qmail has one straightforward sending system that gives clients a chance to handle their own particular mailing records. (2) Different MTAs offer a range of conveyance modes, from fast, unsafe, slow, and queued. Qmail-send is right away activated by new things in the line, so the Qmail framework has only one conveyance mode: fast and queued. (3) Different MTAs incorporate, as a result, a specific variant of inetd that watches the heap normally. Qmail’s configuration inalienably restrains the machine load, so qmail-smtpd can securely keep running from your framework’s inetd.

Proficient: On a Pentium under BSD/OS, qmail can without much of a stretch support 200,000 neighborhood messages for each day. That is separate messages infused and conveyed to post boxes in a genuine test! Albeit remote conveyances are innately constrained by the gradualness of DNS and SMTP, Qmail covers 20 synchronous conveyances as a matter of course, so it zooms rapidly through mailing records. (This is the reason I completed Qmail is because  I needed to get a major mailing list set up.)

Secure: Security is not only an objective, yet a flat out prerequisite. Mail conveyance is basic for clients; it cannot be compromised, so it must be totally secure. (This is the reason I began composing Qmail. I was tired of the security openings in Sendmail and different MTAs.)

Replacement for Sendmail

Qmail underpins: host and client disguising, full host stowing away, virtual spaces, invalid customers, list-proprietor modifying, hand-off control, twofold bob recording, discretionary RFC 822 location records, cross-host mailing list circle discovery, per-beneficiary checkpointing, brought down host backoffs, autonomous message retry plans, and so on. Qmail additionally incorporates a drop-in “sendmail” wrapper with the goal that it will be utilized straightforwardly by your current UAs.

Points of interest of Qmail

Mailing list administration is one of Qmail’s qualities.


1) Qmail gives every client a chance to handle his own particular mailing records. The conveyance guidelines for client whatever go into ~user/.qmail-whatever.

2) Qmail makes it truly simple to set up mailing list proprietors. On the off chance that the client touches ~user/.qmail-whatever-proprietor, all ricochets will return to him.

3) Qmail supports VERPs, which allow totally dependable mechanized ricochet taking care of for mailing arrangements of any size.

4) SPEED – Qmail impacts through mailing records two requests of size speedier than sendmail. For instance, every message on the qmail mailing rundown is conveyed to more than 1000 hosts the world over in only 76 seconds.

5) Qmail consequently forestalls mailing list circles, even crosswise over hosts.

6) Qmail permits unfathomably huge mailing records. No irregular breaking points.

7) Qmail handles associating and sending with the same straightforward instrument. For instance, Postmaster is controlled by ~alias/.qmail-postmaster. This implies cross-host circle discovery additionally applies to false names.

8) Qmail underpins the ezmlm mailing list administrator, which effortlessly and consequently handles bobs, membership demands, and files.


Qmail’s measured, lightweight outline, and sensible line administration make it the quickest accessible message exchange operator. Here’s the manner by which it stacks up against the opposition in five distinctive pace estimations.

Separate local messages: What LSOFT does not tell you regarding LSMTP is what number of isolated messages it can deal with in a day. Does it get stalled as the line tops off? On my home machine, I impaired Qmail’s conveyances and after that sent 5000 separate messages to one beneficiary. The messages were all securely kept in touch with the line circle in 23 minutes, with no lull as the line topped off. After I re-enabled conveyances, every one of the messages were conveyed to the beneficiary’s post box in less than 12 minutes. End-to-end rate: more than 200,000 individual messages a day!

Scheduling: Sent a message to 8192 “trash” beneficiaries on my home machine. Every one of the conveyances were done in an insignificant 78 seconds – a rate of more than 9 million conveyances a day! Contrast this with the velocity publicized for Zmailer’s planning: 1.1 million conveyances a day on a SparcStation-10/50. (My home machine is a 16MB Pentium-100 under BSD/OS, with the default Qmail setup. Qmail’s logs were channeled through accustamp and kept in touch with circle of course.)

Mailing lists with remote recipients: Qmail utilizes the same conveyance system that makes LSOFT’s LSMTP so quick to outgo mailing records – you pick what number of parallel SMTP associations you need to run, and Qmail runs precisely that. Obviously, execution fluctuates relying upon how far away your beneficiaries are. The upside of qmail over different bundles is it’s size: for instance, one Linux client is running 60 synchronous associations, without swapping, on a machine with only 16MB of memory!

Local mailing lists: When Qmail is conveying a message to a post box, it physically composes the message to circle before it declares achievement. that way, mail does not get lost if the force goes out. I took a stab at making an impression on 1024 nearby letter drops on the same plate on my home machine; every one of the conveyances were done in 25.5 seconds. That is more than 3.4 million conveyances a day! Sending 1024 duplicates to a solitary letter box was generally as quick. Contrast these figures with Zmailer’s promoted rate for discarding beneficiaries without conveying the message – just 0.48 million every day on the SparcStation.

General execution: What truly matters is the way well Qmail performs with your mail load. Red Hat Software discovered one day that their mail center, a 48MB Pentium running sendmail 8.7, was coming up short on steam at 70000 messages a day. They moved the heap to Qmail (on a smaller machine, a 16MB 486/66) and now they’re doing fine.

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