Linux Server Details

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===== Postfix_SMTP =====

==== Install as per normal ====
<code>
 apt-get install postfix
 Choose Internet Site Config.

</code>

After Install - Main folder = /etc/postfix\\
Main file = main.cf

====Basic Changes:====
<code>
 Just the name used to identify server
 myhostname = mail.domain.com
 # disable lookup of usernames
 disable_vrfy_command = yes
 Remove hash beside delay_warning_time = 4h
</code>

==== Advanced Changes: ====
<del>
===To prevent cross over emails between multiple domains,===
e.g. where root@mydomain1.net and root@mydomain2.net are on the same server. 
 Add the following line into /etc/postfix/main.cf:
 smtpd_sender_restrictions = check_recipient_access hash:/etc/postfix/restrict

 Create the file: /etc/postfix/restrict
 goodemail@mydomain2.net     OK
 mydomain2.net               REJECT
 
 To activate/ add this file into postfix, type in the shell ->
 postmap /etc/postfix/restrict
Further Details at: http://www.seifried.org/security/index.php/Closet20001122_Postfix_-_The_Sendmail_Replacement,_Part_II
</del>

===== Handle email from Multiple Domains =====
<code>
 vi /etc/postfix/main.cf
 #add in the following:
 virtual_maps = regexp:/etc/postfix/virt/kartbuilding_net
 virtual_alias_domains = kartbuilding.net

 mkdir /etc/postfix/virt/
 vi /etc/postfix/virt/kartbuilding_net
 #add in:
 # Kartbuilding.net mail
 /^email1@kartbuilding.net$/             localusername
 /^email2@kartbuilding.net$/             differentemail@forward.com

 cd /etc/postfix/virt
 postmap kartbuilding_net
 /etc/init.d/postfix restart

</code>

Save and restart postfix. Now the server will handle mail for this domain. No other config required in main.cf. It will deliver it to the localusername or forward it. If an email is sent and isn't matched a 550 will be sent back. This is miles better that the previous postfix/restrict config above.



===== Restrict Mail delivery to Local users =====
On a lists (mailman) server I run - I want to disable mail delivery to local users, however I still want Postfix to deliver mail to /etc/aliases. The line below, which is to be put into /etc/postfix/main.cf  forces postfix to only consult $alias_maps (which is: hash:/etc/aliases ).
<code>
 local_recipient_maps = $alias_maps
</code>

===== Blocking Spam with spamhaus and Postfix =====
This is commonly referred to as a "Postfix anti-UCE configuration" (UCE - unsolicited emails). Postfix, with a very simply modification can block incoming email via spamhaus RBLs (Real Time Black-Hole Lists). The following line is to be added to /etc/postfix/main.cf:
<code>
 smtpd_recipient_restrictions reject_rbl_client zen.spamhaus.org, reject_rbl_client bl.spamcop.net
 #If there are entries already - thats fine, just comment delimit them.
 #Note: sbl-xbl.spamhaus.org has now changed to zen.spamhaus.org as per http://www.spamhaus.org/zen/index.lasso
</code>

The sender is then bounced back an email saying "Blocked by spamhouse" and it is their, or their ISP's responsibility to remove themselves from spamhaus.

**Note:** "ping sbl-xbl.spamhaus.org" wont resolve. What postfix does when checking an ip (e.g. w.x.y.z), is to "ping z.y.x.w.sbl-xbl.spamhaus.org", and if that resolves - that ip is listed as spam. (thanks davisc). <br>
**Note:** Make sure ICMP packets are allowed through the firewall. Otherwise postfix will get a "Destination Not Reachable" and allow the mail through.

See more details at: http://jimsun.linxnet.com/misc/postfix-anti-UCE.txt   and http://www.redhat.com/support/resources/howto/RH-postfix-HOWTO/x441.html and http://www.postfix.org/uce.html and http://www.postfix.org/postconf.5.html#smtpd_recipient_restrictions

Further Info on UCE and Postfix:
<code>
 smtpd_sender_restrictions = Restrictions based in the context of the MAIL FROM command. I.e. restrictions based on who emails are from.
 smtpd_recipient_restrictions = Restrictions based on the RCPT TO command. I.e. restrictions based on who emails are been delivered to.
 smtpd_client_restrictions = SMTP server access restrictions in the context of a SMTP connection request.
</code>
I have found that blocking mails via DNSBL at "smtpd_sender_restrictions" is not always effective as some spammers can forge the MAIL FROM command. "smtpd_client_restrictions" is the first line of restrictions, and ideally the DNSBL blocks should be put in here, however as outlined on http://jimsun.linxnet.com/misc/postfix-anti-UCE.txt , "smtpd_recipient_restrictions" is the best place to place DNSBL blocks.

==== Testing zen.spamhaus.org ====
<code>
 Link: http://www.crynwr.com/spam/
</code>

Simply send an email to the appropriate address on the above website, and it will reply an automated email with the status of whether your email server is blocking correctly using zen.spamhaus.org

Nice :)

====== Debugging and Testing via Telnet ======
SENDING AN EMAIL VIA TELNET 25 & Testing forwarding
<code>
 mail from: sri@mara.net
 rcpt to: user@lastre.com
 data
 .
 quit
</code>

If you get "503 5.5.2 Send hello first", type "ehlo" as the first line after telneting to host 25.

Test and get working Normal - Should be able to send and revieve via pine etc.

Had to adjust /etc/hosts with domain name (this allowed sending emails ok):
<code>
 127.0.0.1       localhost
 136.201.1.250   kartbuilding.net        phidebian
</code>

Good URLS

http://www.muine.org/~hoang/postfix.html

http://www.debianhelp.co.uk/postfix.htm

----

====== Managing Postfix ======
===== Delete an Email from the Queue =====
For Example - sending an email to someone and it bounces. Default retry is for 3 days. To remove it manually :
<code>
 postsuper -d queue_id
</code>

Tons more info at: http://www.postfix.org/postsuper.1.html

===== Delete all Deferred Emails from the Queue =====
If spam emails are been sent and/or your mail queue fills up, you can delete all deferred emails with the following:
<code>
 postsuper -d ALL deferred
</code>

===== Checking Mail logs with pflogsumm =====
pflogsumm shows all the essential information from mail.log. It groups information into the following headings:
  * Grand Totals - messages sent and recieved.
  * Per-Day Traffic Summary
  * Per-Hour Traffic Daily Average
  * Host/Domain Summary: Message Delivery
  * Host/Domain Summary: Messages Received
  * Senders by message count
  * Recipients by message count
  * Senders by message size
  * Recipients by message size
  * message deferral detail
  * message reject detail
  * message reject warning detail
  * smtp delivery failures
  * Warnings
<code>
 apt-get install pflogsumm
 pflogsumm /var/log/mail.log | less
</code>
It is a very useful tool and shows an excellent insight into mail delivery and sending on your server.

===== Show Mail Queue =====
If mails are deferred etc. and you want to see a list of them:
<code>
 postqueue -p
</code>

===== Install Postfix for sending mail via relayhost =====
On one server, I want it to be only able to send emails only. Therefore the following config will bind it to 127.0.0.1 on port 25. It will also be sending emails using a "smart host". Below are the uncommented lines only in main.cf:
<code>
 vi /etc/postfix/main.cf
 smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
 biff = no
 append_dot_mydomain = no
 myhostname = thunder.burkesys.com
 alias_maps = hash:/etc/aliases
 alias_database = hash:/etc/aliases
 myorigin = /etc/mailname
 mydestination =
 relayhost = mail.burkesys.com
 mynetworks = 127.0.0.0/8
 mailbox_size_limit = 0
 recipient_delimiter = +
 inet_interfaces = 127.0.0.1
</code>
It must also be checked on mail.burkesys.com that thunder is allowed to relay emails.

===== Debian Bullseye Config =====
After a new install of debian bullseye, and after setup or [[courier_imaps_server_-_maildir|courier]] and procmail, the following is the config lines added to main.cf (Note: there were minor mods added further for sasl [[setup-config-debian-bullseye#secure_smtpd_using_postfix_and_sasl|see here]] )
<code>
disable_vrfy_command = yes
message_size_limit = 30720000
smtpd_recipient_restrictions = permit_mynetworks,
                                permit_sasl_authenticated,
                                reject_unauth_destination,
                                reject_rbl_client bl.spamcop.net,
                                reject_rbl_client zen.spamhaus.org

virtual_maps = regexp:/etc/postfix/virt/kartbuilding_net,
                regexp:/etc/postfix/virt/sburke_eu
virtual_alias_domains = kartbuilding.net, sburke.eu
home_mailbox = Maildir/
mailbox_command = /usr/bin/procmail -a "$EXTENSION" DEFAULT=$HOME/Maildir/ MAILDIR=$HOME/Maildir
</code>