Unsent message stuck in outbox

I understand there has already been a discussion thread on this topic.
Unfortunately it was closed without a complete resolution.

I have a repeated error message each time I go to check or send mail on my iPhone.
'Cannot Send Mail - You did not specify any recipients'

Each time - there is indeed a message in the sent box with No recipient and No subject.

Deleting this message only solves the problem until the next time I check the mail.

I have updated to the latest Iphone 3G software, reset the phone on several occasions,
and even deleted any recreated the email account.

Has anybody else experienced this problem with email on the Iphone?
Could anyone suggest a possible solution?