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Mojo66
Asked: 2024-12-20 09:08:44 +0800 CST

Postfix/Dovecot: catchall email address exposed in header

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I'm using Postfix to funnel email from three different domains into one catchall like so:

/etc/postfix/virtual:

@domain1.de     [email protected]
@domain2.de     [email protected]
@domain3.de     [email protected]

Sending an email to [email protected] results in the following header:

Delivered-To: [email protected]
Return-Path: <[email protected]>
<[email protected]>
Received: from v2.domain1.de by v2.domain1.de with LMTP id pX7HGJd6ZGcVgBIAGUxxBA (envelope-from <[email protected]>) for <[email protected]>; Thu, 19 Dec 2024 19:57:11 +0000
Received: from mba.domain1.de (home.domain1.de [1.2.3.4]) by v2.domain1.de (Postfix) with ESMTP id 5CF148A278 for <[email protected]>; Thu, 19 Dec 2024 19:57:11 +0000 (UTC)
Received: by mba.domain1.de (Postfix, from userid 501) id 29B953B98524; Thu, 19 Dec 2024 20:57:11 +0100 (CET)

The catchall address is exposed twice. How can I avoid that, preferably by replacing [email protected] with the actual recipient [email protected] ?

postconf -M :

smtp       inet  n       -       y       -       -       smtpd
submission inet  n       -       y       -       -       smtpd -o syslog_name=postfix/submission -o smtpd_tls_security_level=encrypt -o smtpd_sasl_auth_enable=yes -o smtpd_relay_restrictions=permit_sasl_authenticated,reject -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject -o smtpd_sasl_type=dovecot -o smtpd_sasl_path=private/auth
pickup     unix  n       -       y       60      1       pickup
cleanup    unix  n       -       y       -       0       cleanup
qmgr       unix  n       -       n       300     1       qmgr
tlsmgr     unix  -       -       y       1000?   1       tlsmgr
rewrite    unix  -       -       y       -       -       trivial-rewrite
bounce     unix  -       -       y       -       0       bounce
defer      unix  -       -       y       -       0       bounce
trace      unix  -       -       y       -       0       bounce
verify     unix  -       -       y       -       1       verify
flush      unix  n       -       y       1000?   0       flush
proxymap   unix  -       -       n       -       -       proxymap
proxywrite unix  -       -       n       -       1       proxymap
smtp       unix  -       -       y       -       -       smtp
relay      unix  -       -       y       -       -       smtp -o syslog_name=postfix/$service_name
showq      unix  n       -       y       -       -       showq
error      unix  -       -       y       -       -       error
retry      unix  -       -       y       -       -       error
discard    unix  -       -       y       -       -       discard
local      unix  -       n       n       -       -       local
virtual    unix  -       n       n       -       -       virtual
lmtp       unix  -       -       y       -       -       lmtp
anvil      unix  -       -       y       -       1       anvil
scache     unix  -       -       y       -       1       scache
postlog    unix-dgram n  -       n       -       1       postlogd
maildrop   unix  -       n       n       -       -       pipe flags=DRXhu user=vmail argv=/usr/bin/maildrop -d ${recipient}
uucp       unix  -       n       n       -       -       pipe flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)
ifmail     unix  -       n       n       -       -       pipe flags=F user=ftn argv=/usr/lib/ifmail/ifmail -r $nexthop ($recipient)
bsmtp      unix  -       n       n       -       -       pipe flags=Fq. user=bsmtp argv=/usr/lib/bsmtp/bsmtp -t$nexthop -f$sender $recipient
scalemail-backend unix - n       n       -       2       pipe flags=R user=scalemail argv=/usr/lib/scalemail/bin/scalemail-store ${nexthop} ${user} ${extension}
mailman    unix  -       n       n       -       -       pipe flags=FRX user=list argv=/usr/lib/mailman/bin/postfix-to-mailman.py ${nexthop} ${user}

postconf -n :

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
compatibility_level = 3.6
inet_interfaces = all
inet_protocols = all
mailbox_command =
mailbox_size_limit = 0
mailbox_transport = lmtp:unix:private/dovecot-lmtp
message_size_limit = 52428800
mydestination = domain1.de,domain2.de,domain3.de,localhost
myhostname = v2.domain1.de
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
myorigin = /etc/mailname
readme_directory = no
recipient_delimiter =
relayhost =
smtp_tls_CApath = /etc/ssl/certs
smtp_tls_loglevel = 1
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtp_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
smtpd_enforce_tls = yes
smtpd_helo_required = yes
smtpd_helo_restrictions = permit_mynetworks permit_sasl_authenticated reject_invalid_helo_hostname reject_non_fqdn_helo_hostname reject_unknown_helo_hostname
smtpd_recipient_restrictions = reject_invalid_hostname reject_unauth_pipelining reject_unauth_destination permit_mynetworks, permit_sasl_authenticated, check_recipient_access hash:/etc/postfix/rcpt_blacklist
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
smtpd_sender_restrictions = permit_mynetworks permit_sasl_authenticated reject_unknown_sender_domain reject_unknown_reverse_client_hostname reject_unknown_client_hostname
smtpd_tls_cert_file = /etc/letsencrypt/live/v2.domain1.de-0001/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/v2.domain1.de-0001/privkey.pem
smtpd_tls_loglevel = 1
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtpd_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtpd_tls_security_level = may
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_use_tls = yes
smtputf8_enable = no
virtual_maps = hash:/etc/postfix/virtual
postfix

1 Answers

  1. Best Answer

    This is normal and expected behavior. Don't change it unless you know what you're doing, and from the fact you ever asking about it, it seems you don't, so simply don't change this. Also this is only seen by the recipient of the message, if you don't trust your recipients that much, I have a bad news for you. And the user who accesses that mail probably will know that address anyway, because it must be the username to the IMAP server to access the mailbox in the end of the day, right?

    This is used to suppress duplicate delivery. If the mail has the address in the Delivered-To header, it won't be delivered again to that address. It's a feature of local delivery agent, see man 8 local.

    You may suppress it using empty prepend_delivered_header in main.cf:

    prepend_delivered_header =

    RTFM:

    Turning off the Delivered-To: header when forwarding mail is not recommended.

    Instead, it may be better to change frozen_delivered_to to no in main.cf:

    frozen_delivered_to = no

    Then it must not be updated on alias expansion. However, I am not sure how it works, never used it.

    The second instance is in the Received header. Again, blame yourself when you happen to debug your mail if you meddle with this. It's often hard enough even if you have all the bunch of information, let alone when it's deliberately mangled or removed. You can change it with header_checks, see this question.

    Update:

    Apparently, the last (uppermost) Received header was not made by Postfix:

    Received: from v2.domain1.de by v2.domain1.de with LMTP id pX7HGJd6ZGcVgBIAGUxxBA (envelope-from <[email protected]>) for <[email protected]>; Thu, 19 Dec 2024 19:57:11 +0000

    It's hinted by the fact it's recieved via LMTP. Apparently it was added by Dovecot, since it's what the transport to local mailboxes is set to in main.cf:

    mailbox_transport = lmtp:unix:private/dovecot-lmtp

    I did not notice this from the beginning. In that case, you need to setup Dovecot's behavior with adding that Received header. I have no idea how to do this, never used Dovecot myself.

    Also, keep in mind that it probably has no way of determining what the original envelope recipient was, because the alias expansion or whatever Postfix did happened before the message was forwarded to Dovecot. It only knows that the delivery to the catch-all address was requested.

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