For some reason when sending emails from Jira that are in text format, they still sometimes include images of the issue type icons as attachments.
This was reported to me, but at first I couldn't reproduce. Then, without changing anything, it started happening to my test emails as well.
See pictures attached (I don't know why the other example has multiple icons and the other one has only one).
This only seems to be an issue in 7.1 -versions. We reverted back to 7.0.27 where no such issue occurs (using the same template).