We get the following error trying to send emails to clients on a particular domain:
Invalid address: com.sun.mail.smtp.SMTPAddressFailedException: 550 5.7.1 Unable to relay
We've configured our exchange 2013 server with an open relay to allow connections from the Web Help Desk server which authenticates anonymously, the tests work fine and we can send emails to our internal domain without issue. We've recently synced accounts from another external office which uses a different domain but the above error is generated when trying to send an email from a ticket. I've checked settings on the Web Help Desk and that is configured to send emails to any domain.
Any ideas on what am I missing? Thanks in advance!