Email Processor drops the other attachments if there's more than 3
Technically it's not "3" it's whatever number you have on the system settings - misc page, but that's obviously meant to be a limit for activities created through the UI, not to limit what people can email you. It comes up mostly from people who have a large number of graphics in their signatures - you just get their logos and miss the important attachment.
And just to clarify, it's not a display issue, it's actually dropping the attachments and not storing them anywhere.
Will see what I can do...
This goes back to early 4.x at least, maybe earlier, so it's not recent.
As an aside, if anyone knows of a good mail server plugin that strips out graphics in signatures without any false positive removal of real attachments please let me know.