SharePoint Cannot Send Mail to Itself

When using the built-in mechanism to send email from SharePoint (or SPUtility.SendEmail), SharePoint stamps a X-Mailer header of:

Microsoft SharePoint Foundation 2010

If SharePoint is configured to send to the same SMTP service it is set to pick mail up from, SharePoint will drop any message with the above X-Mailer header indicating a possible message loop.

Trevor Seward is a Microsoft Office Apps and Services MVP who specializes in SharePoint Server administration, hybrid scenarios, and SharePoint Online. He has been working with SharePoint for 16 years from SharePoint 2003 on up, managing environments with terabytes of content for 150,000+ user organizations. Trevor is an author of Deploying SharePoint 2016 and Deploying SharePoint 2019. You can find him on Twitter and in /r/sharepoint.