Hmm, very odd.
Does
incoming MMS work?
I'm not sure how it works on Bell, but on AT&T you can send an email to
your_10_digit_mobile_number@
txt.att.net or
your_10_digit_mobile_number@
sms.att.net
For example, if your mobile number is 123-555-1234 then you email
1235551234@txt.att.net and you'd get it as an SMS (text only).
Or if you send a message with a picture attached to
1235551234@sms.att.net you'd get it as an MMS (text+picture).
If incoming MMS message works, then it's definitely an app setting about sending.
Also make sure after you've
activated the appropriate Message Center. It should have a check-mark next to it.
Same with the Access Point, Internet Profile and Browser Account. That should cover everything.
Top Menu > Settings > Applications > Messaging > Multimedia Msg > Message Center
Top Menu > Settings > More > Connection > Access Points
Top Menu > Settings > More > Connection > Internet Profiles
Top Menu > Settings > Applications > Browser > Accounts