Sorry, I have nothing more, if DNS is setup and correct, it certainly should not be stating that it isn't set up, and I have never come across any device that had a bug like that.
If you are setting up GMAIL and the primary DNS is set as 8.8.8.8 then the only way(s) for it to fail is if
1. The gateway is wrong so it can't get to 8.8.8.8
2. Proxy/Firewall
As for setup, with exception to the SMTP server, all the big ones are pretty near identical. So GMAIL is exactly the following
The only change for Office 365 is changing the SMTP server from smtp.gmail.com to smtp.office365.com and of course an email from that service to use. But STARTTLS, port 587 is the defacto standard at this point.
There is a bug in older firmware where Office365 could fail unless you disabled IPv6 (see below), so if you are not on a spar firmware, you may want to update it, or try this:
And change Dual Stack to IPv4
