Support

Unfortunately it's "one of those things". I can tell you that attachments sent by Apple Mail do work and so do attachments sent by GMail. Attachments sent by Outlook sometimes work; apparently different versions of Outlook use different ways to encode them.

Inline attachments (like images pasted in the body of the message instead of being sent as proper attachments) will usually not work.

Further to that, the attached file must comply with Joomla!'s upload criteria. In short, if it's a file that Joomla! would reject if you tried uploading it from the web then it will not be attached when replying by email. This is a major issue when your client is using Windows. For example, Windows does not distinguish between image.jpg, image.JPG and image.Jpg. However Joomla! does. Only image.jpg is allowed to be uploaded. The typical Windows abomination of image.JPG can't be uploaded because the uppercase .JPG extension is actually not a valid extension format. Even worse, Windows does not show the extension and simply tells the client that they are attaching an "image file".

So between the email protocol written 40 years ago to cater for completely different use cases than what we're trying to use it today, MUAs (mail user agents – applications which handle email) doing all sorts of funky crap and Windows being braindead due to its MS-DOS roots it's rather impossible to reliably handle attachments by email.

My rule of thumb is: if you're using GMail to attach a .zip file you're probably OK, but don't count on it. Better upload your files to OneDrive, Dropbox or a similar service and paste a link in your ticket. It's the only guaranteed, cross-platform way to share files in this time and age :(