It is happening because your email has FROM: address <email@example.com>.
Your office SMTP server looks at email coming from the Internet and says: wait a minute! It is office email address, all correspondence sent from it must be internal, how come it is coming from the Internet? Must be fake, must be spammer!
Your tech admin can do the following for you:
- Whitelist blackberry (RIM) SMTP servers
- whitelist your sender email address.
Changing SMTP server at BIS/TMO side, even if it were possible, would not help because your office SMTP server refuses sender email address, not blackberry SMTP server.
To verify, do a quick test: create blackberry email address in your blackberry account, send email from that email address to your office. It should arrive no problem.
That would prove the issue is not SMTP server but sender email address.