A customer went from a server based email to office 365. Of course email gateway stops working. Got settings from their IT vendor and I checked settings on couple of my other customers using Office 365. Everything looks correct, not much info needed.

Error message is consistent "SMTP failed to resolve address of____________Unknown host.

Using Google DNS

Customer is running 4.63 software.

Any thoughts? Thanks.

Is the google DNS reachable from their network? Is the gateway correct? What do you have for the POP and SMTP for outlook?

I'll have to check and see if DNS is reachable. I assume you mean the gateway on the 7100? If so, yes because I can remote in and they are running remote IP Phones.
I'll have to get the POP and SMTP from the IT vendor. Never needed those settings on office 365 before. Thanks.

In 5.6.1 are both your DNS servers set to google? I would use 4.2.2.3 for one of them. I have had very good luck with using level3's DNS server. Also depending on the TLS they are using with Office 365 you might not be able to make it work. Our systems only go up to TLS 1.1 I think. Therefore if they are using the newest one it might cause a issue. That's just an FYI for ya. I normally just use google as a relay account to send emails. It always works without an issue and no headaches.

Turns out we needed to Change the system IP address and reboot the system. Not sure why it worked. I did notice when changing the DNS the restart is quick. IP address restart takes much longer. Maybe just needed a good reboot/ Thanks all.

Reason being is cause on a DNS restart it does a soft reboot. On the IP one it does a reboot as if you would've turned off the system and back on.