Cant send mail

I have tried sending directly and through relays. Neither are working.

When i try to send via a known working relay i get

"Relaying denied. Proper authentication required. (in reply to RCPT TO command)"

When i try to send via postfix directly it automatically bounces back.

I can send to another account on the system however.

Any idea how to make this work?

The relay that's denying you doesn't like the IP you're sending from - and it's probably doing the right thing.

Can you post the info from /var/log/zimbra.log from postfix regarding the bounces?