Check Linux Email

source: linux-troubleshoot-outbound-email/

* check MTA:

ls -l /etc/alternatives/mta

If the command returns a link to “/usr/sbin/sendmail.postfix”, your system is configure to use postfix. 

If it returns a link to “/usr/sbin/sendmail.sendmail”, your system is configured to use sendmail.


* check Relay:

postfix:       grep ^relayhost /etc/postfix/main.cf
sendmail: grep ^DS /etc/mail/sendmail.cf


* mail queue:

mailq

* user mailbox: /var/spool/mail/$USER, /var/mail/$USER