I have recently finished setting a PC at my home as a mail server. I can connect to it with Thunderbird or Outlook because I have Dovecot setup as an IMAP server on the same machine. Also, I have Squirrelmail installed to allow basic webmail access.
I can send and receive emails from both client software and using the webmail fine most of the time. However, this morning I found out that if I send an email through my webmail to the domain UPS.com, I get an immediate 554 error response (SPAM Mail). However, if I send the same email from Thunderbird, it sends just fine.
Any ideas as to how I can make it so that Squirrelmail sends mail so that it is not thought to be SPAM?