When sending mail to certain people from my Blackberry I get the message "Unknow address error 501-'Incorrect address format-on relay of: MAIL FROM:<(my address). There is nothing wrong that I can see with the recipient's address. This occurs when sending mail to some people in my company, but not all. All of us use the same email naming convention.

Any one have any thoughts?

Do you have your compay email address setup as your BB address in the BIS? If so, some companies have spam filters that won't allow another host to send email from a non-company network. Check w/your IT people.