I am hoping that someone can help me send emails from an On-Prem Exchange 2016 Server to Microsoft 365 Tenants. Let me explain.
Angelbeat runs Virtual Seminars for Microsoft. More info at www.angelbeat.com. I setup angelbeatseminars.com to send out newsletters to our 300,000 database of optin email addresses, using a Dell Server running Exchange 2016.
We are having significant problems sending emails from angelbeatseminars.com to Microsoft365 domains; all the emails get delayed/blocked. I have setup angelbeatseminars.com with spf, dkim, reverse DNS lookup, etc. but still it is not working.
Check the header information of one of the delayed email and put the complete header in mxtoolbox analyze header. https://mxtoolbox.com/EmailHeaders.aspx See the hops and you should get some answers where the delay is happening.