I have migrated firewalll policies from my old XTM515 to a new M370, everything looked fine until I realized that my SMTP relay to Microsoft Office 365 was not sending email. Is there some default setting on the M370 causing this issue?
No - the only difference would be possibly different XTM versions.
Did you do a manual migration, or did you save the old XTM515 config to your new M370 using Policy Manager, after changing the firewall model and the Feature Key ?
If a manual one, then try other method, as it could be that you missed something in your manual migration.
I saved the old XTM515 config to the new 370 after changing the feature key, all of the policies seemed to match up but the emails would not send until the XTM515 was reconnected.
Whenever you swap firewalls, reboot your ISP device in case it has an ARP cache for the MAC addr(s) of the old firewall, especially if you have multiple public IP addrs.
Other than that, time to open a support incident.
Relay event log started throwing these errors when the M370 was brought online, the IP address is MS:
Message delivery to the host '220.127.116.11' failed while delivering to the remote domain 'xxxxxxxxxx.com' for the following reason: The remote SMTP service does not support TLS.
The SMTP verb which caused the error is 'STARTTLS'. The response from the remote server is '250-Requested mail action okay, completed
Look at your outgoing SMTP settings for ESMTP, and compare them to the old XTM515 settings.