I'm using MS Outlook 2007. Recently, I have difficulty responding to
people's email to me. I hit Reply, typed my reply message and click Send.
The followng error message pops up:

Your message did not reach some or all of the intended recipients.

553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)

Grateful if anyone can advise.

Thank you

Jimmy