[Exim] prevent delivery via SMTP for a local domain

Hi everybody,

I suppose my problem might be somewhat confusing. Anyway, I hope you
point me in the right direction.

I'm running exim 3.35 on FreeBSD. Before actually delivering mails into
user mailboxes, I'd like to make sure they were changed by an alias file
at least once. To do this, I made up the internal domain mailbox.lmtp,
with my alias files looking like

user1@???    mailboxName

I set qualify_recipient = mailbox.lmtp to automatically append this
domain to the mailboxName on the right side. mailbox.lmtp must be a
local domain to have a director handle the mails.

The director that initiates the actual delivery looks checks for the
mailbox.lmtp domain:

localUser:
driver = smartuser
domains = mailbox.lmtp
transport = lmtpTransport


With mailbox.lmtp beeing a local domain, anybody can telnet to the
mailserver's smtp port and inject mails for <boxname@???>
directly.

Is there any way to prevent this? I thought of the global filter, but
there's no way to check the recipient.

Any ideas?

Martin

--
Martin Kaiser                 Tel.  : +49 69 7589 150,  +49 173 8626814
Plus.line AG                  Fax   : +49 69 7589 1533
Mainzer Landstr. 222-224      EMail : mk@???
D-60327 Frankfurt am Main     WWW   : http://www.plusline.net