027-779 is an authentication error while 016-781 is a connection to the server error. The fact that your code changed to 027-779 means that you're hitting the SMTP server now. It seems like your getting a server side rejection because, if the machine couldn't understand the response from the server in regards to authentication, you would most likely get an 027-777 (server does not support SMTP Auth) code. I recommend testing temporarily with a GMAIL account because the requirements are generally the same as Office365 (STARTTLS, enabling SMTP Auth aka 'Allow Less Secure Apps') so if it works than you'll want to focus on Office365 side reasons for the failures.
If you really want to go deep you can enable the network troubleshooting log (pcap) feature and take a packet capture that you can review in WireShark.
That function is enabled in System->Security->Feature Enablement
The code to enable the function is *3005414141
To disable it the code is *3005414140
Once enabled you can start a capture by navigating to System->Logs->Network Troubleshooting
Understood. If you can tell us the 6 digit (xxx-xxx) fault code and/or message that occurs when a test fails that'll be helpful. I had a hard time with an Office365 SMTP setup recently and it was on the Office365 side. We were using an account that hadn't been used as an email service account before, and by default SMTP Auth was not enabled for that account. I had to work with the admin to enable SMTP Auth for that user account and then voila, all of our MFD's started sending email. The link below says how to check that.
Note: In the instance that I referenced the account actually showed SMTP Auth as enabled but a company wide policy had overwritten that after it was created. We had to toggle it off and on again and then it worked.
Thanks for the suggestion. That was the last setting I verified after I found an obscure post about it. We had that set and selected. Then I posted my cry for help. :)
Have you configured the wireless network as the primary network? I find that to be the most commonly missed step when configuring scanning services via WiFi. Outgoing connections only go out over the primary network and that defaults to Ethernet. See the guide at the link below for where to find that setting.
Note: If this is the problem you are probably receiving an 016-xxx error code when scanning which indicates a problem connecting to the SMTP server.
So my co-worker and I have come across an issue where we cannot set up scan to email on a wireless Xerox 6515.
Credentials are correct,
DNS and IPs appear fine (192.168.x.x)
Using port 587
Printer Firmware is up to date.
With all the similar messages on this forum, I'm surprosed Xerox doesn't have a moderator that would create a doc that would help us all. It is obvious this issue has stumped some talented IT professionals.