Here are a few handy items for Postfix email server users:

1. If your system is acting as a spam / antivirus / relay server for secondary internal servers, and your destination mail server is down, postfix will queue your messages to resend at a later time. In order for postfix to instantly re-queue these messages you use:

postqueue -f

2. The mailq equivilant specific to postfix is

postqueue -p

3. If you want to delete specific messages in your queue, use an ncurses based open source software called pfqueue. It will give you a menu that shows mail currently queued, and allows you to delete specific emails.