Several of our customers and suppliers use messagelabs and are unable to send or receive email from our domain (thesolution.co.uk) consitstently. They are receiving the generic 553 message. Our SPF and DKIM records are intact, and mail is coming from legitimate accounts.
We have tested what messages can get through and it appears to be linked to the e-mail address of the sender being part of our standard signature.
Once we removed the e-mail address from the signature we appear to be able to send, but the customer then receives the error when attempting to reply.
This seems to be a problem with the content triggering the filtering.
We have checked that we are not listed on any blacklists either ip based or domain based.
Can you please explain how we can identify the problem.