I have an old VOIP system that sends voicemails as email links/attachments ...
the FROM address (prefix) is always email@example.com
How do I allow IIS's SMTP virtual server to relay (to Office 365) with the FROM address constantly changing?
All devices can relay just fine.
Only this VOIP system is an issue (where I cannot keep the "FROM email address" constant)
Until now, I always used scenario 2 in this guide to successfully setup SMTP relay with Office 365:
Toshiba Strata CIX
Stratagy ES Voice Mail Application