RE: NAV 2017 Approval Notification Email issue
Hello,
Assuming you are using Exchange Online, is there a third-party connector installed that modifies the header of the message like a third party tool that adds a signature to it.
Because you are working with Dynamics NAV 2017, you are using basic authentication in Dynamics NAV. This also means you can use PowerShell to send the mail to Exchange Online. If that fails as well, it is an issue with Exchange Online.
Some partners / customers use the xxx.mail.protection.outlook.com over port 25. Many ISP's block port 25. You only need to configure Dynamics NAV with the following settings:
smtp.office365, port 587, UseSSL: true and then an Exchange Online licensed user plus the user's password or an App password. All users needs to have SendAs permissions to send as the SMTP user.
What could go wrong is that in your DNS the MX record is not configured correctly or you are using the workarounds defined in the following article (there is no need to go through this article, the scenario works out of the box):
learn.microsoft.com/.../how-to-set-up-a-multifunction-device-or-application-to-send-email-using-microsoft-365-or-office-365
Yes, I agree with the Microsoft answer. It usually is external to Dynamics NAV and a configuration issue either in Exchange Online or in your DNS (or there is a third party connector that does a few tricks with the message header). You can easily verify this with Exchange message trace. Windows Security may also have a spam policy in place that does tricks with the message header, there is no need to whitelist Dynamics NAV.
If you can repro the scenario with smtp.office365.com, port 587 and SSL enabled using PowerShell, you can present that to the Microsoft Exchange team.
Hope this helps alreaady.