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I want to make Exim perform recipient verification with a callout to the LMTP server during processing of the RCPT ACL.

I have the following router:

    domains = +virtual_domains
    driver = accept
    transport = dovecot

and transport:

    driver = lmtp
    socket = /var/run/dovecot/lmtp

When ACL processing reaches the following statement:

    domains = +virtual_domains
    verify = recipient/callout

the callout is not attempted:

$ exim -d -bhc
>>> using ACL "acl_check_rcpt"
processing "warn"
check domains = +virtual_domains
cached yes match for +virtual_domains
cached lookup data = in "+virtual_domains"? yes (matched "+virtual_domains" - cached)
check verify = recipient/callout
--------> virtual_account router <--------
checking domains
cached yes match for +virtual_domains
cached lookup data = in "+virtual_domains"? yes (matched "+virtual_domains" - cached)
R: virtual_account for
calling virtual_account router
virtual_account router called for
  domain =
queued for dovecot transport: local_part = test
domain =
  errors_to=NULL localpart_data=NULL
routed by virtual_account router
  envelope to:
  transport: dovecot
Cannot do callout: neither router nor transport provided a host list
----------- end verify ------------
warn: condition test succeeded in ACL "acl_check_rcpt"

I guess the lmtp transport is unable to do callouts, but I'd appreciate a second opinion.

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1 Answer 1

up vote 2 down vote accepted

AFAIR Exim can do recipient email verification via LMTP over internet socket (you use Unix socket).

Exim LMTP callouts for recipient existence verification - The document describes how to make Exim4 check in real time presence of Cyrus (IMAP) mailbox using exim's (LMTP) callouts.

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That did the trick! The only disadvantage is that now my LMTP server is exposed to any process on the system. Fortunately iptables can help here: iptables -A OUTPUT --out-interface lo --protocol tcp --dport 24 --match owner ! --uid-owner Debian-exim --jump REJECT --reject-with icmp-admin-prohibited prevents ant other processes from interfering with the LMTP service on port 23. –  Sam Morris Jul 31 '13 at 2:07
You may consider reporting it a the bug (no verification over Unix sockets). –  Andrzej A. Filip Jul 31 '13 at 4:18
In fact I found this bug while searching: <>;. Shame their robots.txt file prevents search engines from indexing the bugs. :( –  Sam Morris Jul 31 '13 at 12:47
It is a pretty old wish (year 2004) :-) –  Andrzej A. Filip Jul 31 '13 at 17:54

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