Exchange send connectors in hybrid environment

Copper Contributor



I have an Exchange 2010 box (I know! soon to be replaced) on-prem, configured as a hybrid. All mailboxes are Exchange Online. I use the on-prem to relay mail from scanners and some apps but I'm getting a few errors.


The send connector created by the Hybrid Config Wizard is configured to route to a smart host on-prem which in turn should route to EOL via ProofPoint. The problem I have is, when I try to scan to email, I get an invalid certificate error even though I have a valid cert with a subject which matches the email domain.


If I change the TLS setting for the send connector to remove the need for certificate exchange (i.e. TLSAuthLevel on the connector is set to EncryptionOnly. The message does leave my organisation but the receiving smart host rejects the mail and sends an NDR with '550 5.1.10 RESOLVER.ADR.RecipientNotFound'.


The recipient I'm sending to is an remote user mailbox and I can see that remote user mailbox on my Exchange On-Prem. It's working fine (I'm trying to send a mail from the scanner to myself). 


Any thoughts as to why this might be happening?




1 Reply

Hi @PMC15

If you want to setup SMTP relay in hybrid exchange environment i would recommend to use SMTP IIS virtual Server you will avoid too many complicated scenario.

How to Set SMTP relay on iis , useing 365 mail - Microsoft Q&A



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