5.1.0 - Unknown address error 550-'relay not permitted'

[cobro]

The following message to <user@domain.net> was undeliverable.
The reason for the problem:
5.1.0 - Unknown address error 550-'relay not permitted'


How can i fix this there is only 2 domains on my server that works other do not work

plz help
Thank you all do much for your help here

[thewebhostingdi]

Please make sure that the domain entry is made on /etc/localdomains and not on /etc/remotedomains.

[cobro]

all domains in /etc/localdomains and no in /etc/remotedomains

[cobro]

This was the whole time simple dns issue so if you have similar problem then go over your dns thoroughly.