503 User not found

[Help me please]

When I send an e-mail to people I always get a message thet my e-mail was
undeliverable because the user was not found (503). How do I fix this
Thanks

 

[dlw]

that message is from the emal server at the other end telling you the address
you are sending to is wrong, the part before the @whatever.com is the user
name and it is incorrect.