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Office 365: Hybrid Setup – Connector Validation Failed

While setting up a Hybrid Solution today, Office 365 Outbound Connector validation failed. This is simple solution be I could not find a proper blog so I am sharing the solution.



Connector Validation failed and given the following error:


450 4.4.101 Proxy session setup failed on Frontend with ‘441 4.4.1 Error encountered while communicating with primary target IP address: “Failed to connect. Winsock error code: 10061, Win32 error code: 10061.” Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. The last endpoint attempted was IP address




Connector Validation wizard try to connect to the SMTP server and send the email. So Hybrid configuration wizard will configure everything for you but can’t open a port on the firewall.

In this setup SMTP server is a Hybrid server which had not opened port 25 from firewall.



Telnet to the SMTP server fqdn failed from the Internet.

We forgot to open the port 25 pointing to the SMTP FQDN mentioned in the connector at the firewall level.

Opened the port 25 and Validation was successful.


Prabhat Nigam

Microsoft MVP | Exchange Server


Tweet me @PrabhatNigamXHG

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