Postfix is unable to send e-mail to aliases.
 

All my websites and even the SMTP server is unable to send an e-mail to an alias. It just errors out.

Is there any way to correct this?

As usual, post the exact error message from the mail log if we shall be able to help you.

I actually figured this out.

For those having the same problem.

We use an external server for our domain registration and DNS settings. We were also using them for our e-mail forwards. However, when using ISPConfig to send outgoing mail to these forwards we needed to set these forwards within ISPConfig as well.