We have an issue with single company trying to email us. The failure code is #4.4.1 which means a connection time-out. However, to my knowledge no one else that is emailing us is having this issue.
They sent me the bounce-back and the generating server was their email server. However, one line of it I'm unsure about:
Final-recipient: RFC822; email@example.com
Maybe they typo'd the email address or something? I read that 5.4.0 means the address was not found on our email server.
Is this issue on our side or theirs? What (if anything) can I do to help fix this? We have on-premise Exchange 2007 (in an SBS 2008 VM).