#5.7.1 smtp;550 5.7.1 Unable to relay

[coch]

Am starting to get a number of these NDR's when people reply to an email. We have not changed anything on our SMTP connector, DNS etc Does anyone have any idea why this would happen and know of anything I can tell my customers to do
At present if click on resend it seems to go ok and if generate new mail message it seems to go ok -- very frustrating!

 

[JimWells]

How is your SMTP server configured? Send directly to remote hosts using DNS? Smarthost?

Do you know if you have a reverse lookup entry in DNS for your outgoing SMTP server?


Might also check your outgoing server's public IP at

http://www.ordb.org/lookup/