I blame weak morning coffee for the oversightIncluding your OS X version and some other basic details would help.
Maybe this, even if it's an old thread?
https://discussions.apple.com/thread/3395892?start=0&tstart=0
Yes using the default Mac Mail app.OK, but are you:
- using Mail as the default email app.?
- is the Mail account POP or IMAP?
- are you perhaps using iCloud or as a share base or some such?
- checked the Mail account settings and your iPhoto preferences settings?