SmarterMail 16 makes exclusions now for .GRP, .CFG, .EML files. This won't affect the spool but we did these other filetypes because we noticed some slowdown involving Defender when doing heavy I/O related stuff in mailboxes, Moving large amount of emails, etc.
I could understand doing the spool but I could see Defender possibly blocking things it sees coming into the spool. Not sure if its something we'd wanna do automatically but I could see about having this suggestion put into our help documentatio. Thanks for bringing it up.