SharePoint Cannot Send Mail to Itself23 Mar 2013 | SharePoint 2010
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.