Also, OS X latest, FileMaer 13 latest, FileMaker Server latest. Also a problem with v12. Not sure what kind of email server SMTP sends to.
With six Send Mail steps as shown below, the two with both an attachment and a message are never received, while the other four are always received. Note the pauses so the email server does not detect as spam.
Running this several times as a server script gives the same results.
Running several times on local FMP = same results.
Problem "solved." I had to switch to another email that has a different SMTP provider. The non-working account must have some kind of filter that catches a combination of message and attachment as spam. Even adding char (13) or other combos after the message did not work.
It is either use a specific email account, or send two emails, one with the message and one with the ttachment (or maybe a long subject line.)