We run exchange, but all our emails are routed through a 3rd party mail service, which filters, scans etc.
We have 3 domains that we receive email on, lets call them ADomain.co.uk, BDomain.co.uk and CDomain.co.uk.
We own and look after the domain names. But we pay a 3rd party company to host the websites and just point the domain names to the websites.
There is a webform on one of the websites adomain.co.uk, that can be filled in, it should then post the details of the form to us at email@example.com, however we never receive that email.
If they change the address to point to any other address like a gmail or hotmail address it works.
If I email the firstname.lastname@example.org address from a different external account it works, but the email from the hosted site to any of our domains, a, b or c, never comes through and our mail host has no record of a connection attempt being made.
By changing the user account that it sends from to a gmail account we finally get a NDR:
Mail Delivery System
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
email@example.com No Such User Here
The email address (and we've tried several, at all 3 domains) is correct. Noone else has any trouble emailing the domains. the hosting company have no trouble emailing anyone else other than us. Can anyone explain what's going wrong?