Check if email address exists (not if email addrss is valid)

Ryan Heath wrote:
> Or you could use the SMTP protocol to verify the
mailbox existence.
> After sending the RCPT TO message, you can close the
conversation,
> without actually sending an email.
>
> A lot of examples of programming the SMTP protocol in
C# can be find
> on www.codeproject.com
>
> // Ryan
>

You can do that - but a lot of mail systems will consider
that abusive,
and will automatically add your IP address and/or hostname
to blocking
lists. They have no way to distinguish that from a
dictionary attack run
by spammers to harvest addresses.

Just a thought...