Hybrid connector not working - Negotiation failed

Question

Hello,

We noticed an issue this morning that our emails are stuck in mode "Pending". When doing a trace on Office 365 Exchange Admin Center, we are seeing this error LED=450 4.4.317 Cannot connect to remote server [Message=451 4.4.0 TLS negotiation failed with error TimedOut. We use a connector to send the emails back to our on premise server to apply a signature. It seems the email is not even hitting our On Prem server because I have nothing in my Exchange Queue log.

Not all emails are getting stuck with this error, it’s very hit or miss. I ran the Test Connectivity Analyzer on the Microsoft site and we are not seeing any issues on this site. When running a validation on our mail flow connector, sometimes both tests pass and sometimes the send test email fails but the check connectivity always succeeds. We haven't done any recent changes to our Exchange server in a while and this has been working flawlessly for a few years.

Any help would be appreciated to get me into the right direction!

Thank you!

Answer 1

Currently it seems hard for us to further troubleshooting because it didn’t occur to all the emails. Did you find any obvious differences between these emails and normal emails?

 

“We use a connector to send the emails back to our on premise server to apply a signature.” Did you use the connector created by HCW? And how do you apply the signature? You could re-run HCW and only use the connector created by HCW, then check if the issue persist.

 

The network traffic communication between the Exchange Online and Exchange on-premises via TLS, as far as I know if the on-premises firewall which may affect the traffic and would cause this problem. So if possible and convenient, please try temporarily disable the on-premises firewall on a non-work time to see if it helps, thanks.

 

 

Answer 2

Hello,

Thank you for your help! The issue ended up being a Firewall issue and we had to update our IP range using the Microsoft Documentation https://learn.microsoft.com/en-us/microsoft-365/enterprise/urls-and-ip-address-ranges?view=o365-worldwide