Dear Sirs,
this is a simple how to for Checking and setting postfix maximum queue lifetime or timeout:
1. How to see the default settins: as root give:
postconf -d maximal_queue_lifetime
(Default is 5 days).
2. Using the below command purse the main.cf file to see what is the setted value:
postconf | grep maximal_queue_lifetime

3. If you want to change ex to three days give the command:
postconf -e 'maximal_queue_lifetime = 3d'

The postconf -n command shows the settings that are currently configured in /etc/postfix/main.cf, whereas the postconf -d command shows the default settings that are valid unless something else is set in /etc/postfix/main.cf.

So, to find out about the current value of maximal_queue_lifetime, you can run the commands:
postconf -d | grep maximal_queue_lifetime
postconf -n | grep maximal_queue_lifetime

Best Regards,
Mike Kranidis