This issue is mentioned in the comments by @Halley on JRA-1898, a rather old feature request. But I believe it's somewhat different than that issue and really should be filed by itself as a Bug.

Jira’s comment notification system isn’t really reliable because we can’t depend on users getting comment notifications all of the time.

We have set up a notification scheme that sends an email notification to all issue watchers and the issue assignee whenever anyone makes or edits a comment on the issue. This works fine when someone adds the comment from within Jira itself.

We also allow users to email back a reply to these notification emails, and we're set up so their email replies are added to the issue as and additional comment. This too works.

What doesn't work is, if a user includes any kind of attachment, regular or inline, in the reply email, Jira will not send a notification email that there is a new comment. If the user deletes all attachments, images, etc. before sending it, however, and just sends text in the reply, Jira will send out a notification. Either way the comment is still being added to the issue. It's just a problem with the notifications not being sent out unless the comment contains only text.

The problem is Jira assumes that anything that isn’t text in the email is an attachment. That includes things that aren’t really attachments, like inline images and logos that appear in the message or in a sig. Also, since every notification that Jira sends out has icons and logos in it, simply replying to these sends back a message full of “attachments,” thus defeating the comment feature and filling up the issue with garbage “attachments” that really should not be part of the issue record.

I can ask users to delete everything except their text reply when replying to a comment via email, but this isn’t really practical since, of course, your average user won’t remember to do that. Also, sending out a notification every time an issue is updated doesn’t work for us. Users will get way to many notifications over the course of the issues’ life, most of which they will not understand. We really just want to notify them of all new comments.

I see two possible solutions (this is in order of my preference)

1. If Jira had a setting to block attachments via email that would solve this problem (I know JEMH can do something like this, but its price is very high to use for only this purpose).

2. If Jira could be set to ignore any email attachment with “Content-Disposition: inline”, I think this also would fix this problem. If its “Content-Disposition: attachment” it should add it to the issue, but ignore otherwise.

BTW all users here have a Jira account, and this does not seem to be related to their "my changes" selection under their profile settings. Notifications aren't going out to anyone in these cases, regardless if they sent the reply or not.