https://kb.unixservertech.com/ 2026-05-12T21:23:30+00:00 https://kb.unixservertech.com/ https://kb.unixservertech.com/_media/wiki/dokuwiki.svg text/html 2019-06-06T21:50:01+00:00 Anonymous (anonymous@undisclosed.example.com) https://kb.unixservertech.com/software/postfix/authenticated_relay?rev=1559857801&do=diff Authenticated Relay with Postfix Unix servers generally come with some kind of mail server installed. This is used to send mail generated by the system for log reports, error messages, etc... By default, it goes to the root account on the local server, but this requires a technician to log into each server and manually check mail. It is much better to have all mail forwarded to one or more e-mail accounts. See text/html 2020-01-03T04:13:10+00:00 Anonymous (anonymous@undisclosed.example.com) https://kb.unixservertech.com/software/postfix/dkim_dmarc?rev=1578024790&do=diff Securing SMTP Server DKIM Generate DKIM keys Basically, all you do is generate a public key pair and put the public key part (in ASCII) into a specially formatted TXT field in the database. Then, add the private key to your mail server. See: <https://www.mailhardener.com/kb/how-to-create-a-dkim-record-with-openssl> Validate DKIM text/html 2020-09-24T00:09:28+00:00 Anonymous (anonymous@undisclosed.example.com) https://kb.unixservertech.com/software/postfix/quickreference?rev=1600906168&do=diff Postfix Quick Reference This is just some notes on things I do in Postfix. Finding User who has been hacked * look for messages that are sending to multiple recipients grep 'postfix/smtp' /var/log/mail.log | cut -d ':' -f4 | grep -v 'connect' | grep -v warning | grep -v SSL | sort | uniq -c | sort -nr | head text/html 2019-06-06T21:49:10+00:00 Anonymous (anonymous@undisclosed.example.com) https://kb.unixservertech.com/software/postfix/root_email?rev=1559857750&do=diff Handling System E-mail Unix servers generate a lot of e-mail, with most of it being sent to the root user's mail account. When you have more than one or two servers, logging into each and checking mail (generally from the command line) is not effective. Instead, it is better to forward all system e-mail to a centralized account which can then be checked via normal procedures, for all servers set up this way. text/html 2019-06-06T20:39:57+00:00 Anonymous (anonymous@undisclosed.example.com) https://kb.unixservertech.com/software/postfix/start?rev=1559853597&do=diff Postfix Postfix is an SMTP server for Unix. It is very light weight and extremely configurable, with tons of documentation and addins available.