I have the Postfix/Courier/Amavis/Squirrel running on an Ubuntu 10.04 box. The GUI is enabled. And giving the update notice, one of which is MySQL 5.1 Will it break the system if I click upgrade? Doing so for PHP on one of my boxes made a real mess for websites using deprecated commands.
The upgrade should be no problem (unless you added third-party repositories to your /etc/apt/sources.list).