Wirelessly posted (HTC Touch Pro 2: Opera/9.80 (Windows Mobile; WCE; Opera Mobi/WMD-50369; U; en) Presto/2.4.13 Version/10.00)

I just tried sending an e-mail from Outlook using my Gmail to another Gmail, and the size was 8MB. I got an error, then reduced the attachment size below 5MB and it sent. How do I change the send size limit? I've received about 15MB through Gmail to Gmail before, so there must be some setting on the phone (not mail server side).