I'm new to Outlook Express and was getting along fine until yesterday!
I sent three separate emails to people who I email on a regular basis, they
all replied (with my original email still showing) and I replied to them
(with both previous emails showing). I then received three emails from my
Mail Delivery System, Subject "Delivery Status Notification (Failure)"
When I opened each email, it said that the email was undeliverable and the
reason for the problem was:-

5.1.0 - Unknown address error 550 - "Rejected"

I haven't been able to find out why this is happening and it is driving me
nuts!

Please, please can somebody help me!

Thanks