I Installed squirrel mail on along with ispconfig 3on my VPS. I was able to set up squirrelmail with no issues and sent a test email to a few accounts. It says sent but the receiver doesn't get the mail the same is for reverse. I tried mail forwarding and that works. As in I would set it so that if my squirrel mailbox got a message it would forward it to a secondary email. I still would like the original mailbox to work how do I address this issue?
Are you able to send and receive emails with webmail? An easy test if the local mailsystem works is to login to webmail with a account hosted on the server and send a email to the same address that you used to login to webmail. The email shall arrive within a minute back to your account when the local mailsystem works. If the email does not arrive, then check the mail.log Post the error message(s) that you get in the mail log file when the problem occurs. The mail log file is in the folder /var/log/, it is named "mail.log" on Debian and Ubuntu Linux and named "maillog" on other distributions.
