Cannot send email from list to another list
I found via Microsoft SharePoint Support that sending an email through SharePoint workflow from a list to another list/library is not allowed by design. When initiated, SharePoint inserts this header to the eml file - "X-Mailer: Microsoft SharePoint Foundation 2010" - and the timer job won't pick up the file from the Drop folder. If you remove the string by hand, it immediately picks it up and delivers it to the destination. Same thing occurs with the SPUtility.SendEmail method (PowerShell outputs a message that says "processed successfully" but it never sends it to the destination until you manually remove the header info). Please not that the source and the destination are two separate lists. By the way, the X-Mailer header shows "2010" for both 2013 and 2016 version of SharePoint.