If the attachment is has a .EML file extension, it can't read them. Most of the time though, it would say that it's 0 KB.
What kind of attachments are they?
how are they jpegs if it shows EML extensions? are you sure the connection is not getting interrupted or are you using a different email protocol
The OP didn't say they were EML files, that was someone else asking a question, I think.
Anyway, I just sent myself two emails, each with a different .jpg attached. I had no trouble opening either of them, and viewing them with the Gallery app.
I'm using the stock htc app. I haven't tried gmail with jpgs, although I've gotten other attachments on gmail without issue.
A couple of thoughts: I'm using htc mail to get my work EAS (Outlook) email. I suppose Pop3 could handle things differently.
I have "Attachment Cache" set to the SD card, not internal memory, and "include file attachment" set to Never. So I have to manually download the attachment after opening the message.
Check those settings, and if they're different than mine try changing them and see what happens.
Can't think of anything else to offer. Sorry.
Weird. I have none of those problems. What phone are you using?