In article ,
:::Jerry:::: wrote:

So do explain why mail can be returned to the sender up to a week
after the mail was sent to a invalid and non existent address......

If the email was sent to an invalid, non existent address and took a week
to bounce then the mail server is broken.

If (as others have said) it the domain is valid then the mail system will
attempt to deliver it to the mail machine(s) at that domain. If the
address is invalid then ideally the remote machine should not accept it
and should reject at SMTP time with a permenant error (5**) to cut down
on collaterol spam but several systems out there are broken and accept and
then bounce. Should still be pretty instant though. If the remote mail
system accepts the email and then takes a week to bounce it it must have
been sent to an address that is valid (many domains run catchall addresses
for example). A mail system will not keep retrying a non existant address
for a week - it has nothing to retry! (unless it is very, very brain dead).

Darren