{"id":914,"date":"2012-08-02T16:12:06","date_gmt":"2012-08-02T08:12:06","guid":{"rendered":"http:\/\/rmohan.com\/?p=914"},"modified":"2012-08-02T16:14:02","modified_gmt":"2012-08-02T08:14:02","slug":"qmail-how-does-it-work","status":"publish","type":"post","link":"https:\/\/mohan.sg\/?p=914","title":{"rendered":"Qmail : How does it work ?"},"content":{"rendered":"

Qmail : How does it work ?<\/h3>\n
<\/div>\n

Qmail programs & configuration files
\nQmail works using about 15 small programs. It also uses a pretty large number of configuration files. At the beginning, this may appear as quite confusing. Once you are familiarised with these configuration files & programs, qmail administration will be easier.<\/p>\n

Qmail programs<\/p>\n

Qmail continuously runs 5 daemons. Remaining 10 programs are launched by these 5 daemons as and when required.<\/p>\n

Let us see which are the 5 daemons.<\/p>\n

1. qmail-send
\n2. qmail-lspawn
\n3. qmail-rspawn
\n4. qmail-clean
\n5. tcpserver<\/p>\n

How Qmail works<\/strong><\/p>\n

1. Email arrival in Qmail<\/strong><\/p>\n

Mail arrives in Qmail in two different ways.<\/p>\n

(i) Locally injected emails.<\/p>\n

There is a program called sendmail that comes with qmail. It is a program that mimics functionality of legacy sendmail, its arguments are also similar. sendmail accepts the local email and passes it to qmail-inject.<\/p>\n

(ii) Remote emails arrived via SMTP<\/p>\n

* tcpserver listens incoming connections on the SMTP port.
\n* upon a new SMTP connection, qmail-smtpd is launched.
\n* qmail-smtpd receives emails via SMTP.<\/p>\n

2. Queuing emails<\/strong><\/p>\n

* qmail-inject & qmail-smpd pass received emails to qmail-queue.
\n* qmail-queue places emails in the folder \/var\/qmail\/todo
\n* qmail-queue adds necessary headers to emails
\n* Then, it notifies qmail-send about newly queued emails.<\/p>\n

3. Processing queued emails<\/strong><\/p>\n

* qmail-send takes the message out of \/var\/qmail\/queue\/todo folder
\n* qmail-send checks the recipient address of the email
\n* If the recipient addres is local, email is passed to qmail-lspwan
\n* If the recipient address is remote, email is passed to qmail-rspawn<\/p>\n

4. Email delivery to local and remote recipients<\/strong><\/p>\n

* qmail-lspawn passes email to qmail-local
\n* qmail-local delivers email to local email address
\n* qmail-rspawn passes email to qmail-remote
\n* qmail-remote connects to remote mail server and delivers email to remote email address<\/p>\n

5. Cleaning queue after delivering emails<\/strong><\/p>\n

* Once all messages are delivered, qmail-send notifies qmail-clean
\n* qmail-clean removes the delivered emails from the queue<\/p>\n

Qmail configuration files<\/strong><\/p>\n

Qmail configuration files are located in the folder \/var\/qmail\/control.<\/p>\n

1. badmailfrom
\nAll “from addresses” which are blacklisted.<\/p>\n

2. bouncefrom
\nIt is the bounce email from address. Usually it is “mailer-daemon”.<\/p>\n

3. bouncehost
\nIt is host name of server<\/p>\n

4. concurrencyincoming
\nMaximum number of simultaneous incoming SMTP connections allowed.<\/p>\n

5. concurrencylocal
\nMaximum number of simultaneous local deliveries<\/p>\n

6. concurrencyremote
\nMaximum number of simultaneous remote deliveries<\/p>\n

7. defaultdomain
\nDefault domain name of server<\/p>\n

8. defaulthost
\nHost name of server<\/p>\n

9. databytes
\nMaximum number of bytes in message (0=no limit)<\/p>\n

10. doublebouncehost
\nIt is the bounce email from address. Usually it is “mailer-daemon”.<\/p>\n

11. doublebounceto
\nIt is the bounce email to address. Usually it is “postmaster”.<\/p>\n

12. helohost
\nIt is the host name used in SMTP HELO command<\/p>\n

13. idhost
\nIt is host name of server. It is used when creating Message-ID.<\/p>\n

13. localiphost
\nIt is local IP address<\/p>\n

14. locals
\nList of all local domains.<\/p>\n

15. me
\nIt is the hostname of server<\/p>\n

16. morercpthosts
\nOnly 50 domains can be added in rcpthosts, remaining domains should be in morercpthosts.<\/p>\n

17. queuelifetime
\nIt is the number of seconds an email can remain in queue<\/p>\n

18. rcpthosts
\nDomains of all locally hosted email addresses.<\/p>\n

19 smtpgreeting
\nIt is the SMTP greeting message used by mail server.<\/p>\n

20. timeoutconnect
\nTime in seconds, the server has to wait for SMTP connection<\/p>\n

21. timeoutremote
\nTime in seconds, server has to wait for remote server<\/p>\n

22. timeoutsmtpd
\nTime in seconds, server has to wait for SMTP client<\/p>\n

23. virtualdomains
\nList of all virtual domains<\/p>\n","protected":false},"excerpt":{"rendered":"

Qmail : How does it work ? <\/p>\n

Qmail programs & configuration files Qmail works using about 15 small programs. It also uses a pretty large number of configuration files. At the beginning, this may appear as quite confusing. Once you are familiarised with these configuration files & programs, qmail administration will be easier.<\/p>\n

Qmail programs<\/p>\n

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