I have SquirrelMail version 1.4.6 [CVS]-0.cvs20050812.1.fc4 and use Fedora Core 4. Dovecot is up and running and I can connect with email clients like thunderbird or kmail from localhost. Do I have to edit any special config-file for SquirrelMail which is new for FC4?
IS SELinux your problem? To see if SE linux is enabled on your machine, su root and type: /usr/sbin/sestatus -v. To test if SE Linux is your problem you can temporarily turn it off by typing setenforce 0. Then test your mail server. (and type setenforce 1 to temporarily restore enforcing mode after you have concluded your test).