Original: badrcptto-v1.02.netqmail.patch

The badrcptto patch SMTP-rejects email for specific recipients in an
email domain you otherwise accept mail for. List these "bad recipients"
in control/badrcptto, one per line.

Rejection occurs during the smtp envelope (rcpt) phase, before the email
headers and body can be transmitted.

Alex Kramarov added code to skip badrcptto checks if RELAYCLIENT is
set, so that one could prevent remote users from sending email to
certain local accounts while permitting local users to do so. This has
been merged.

Andrew McCarthy added logging for badrcptto hits. This has also
been merged.

Original: https://www.soffian.org/downloads/qmail/qmail-smtpd.patch

This patch modifies qmail-smtpd to check for an environment variable,
$RCPTCHECK. If it is set, for each 'rcpt to:' that qmail-smtpd receives,
it will fork/exec $RCPTCHECK. $RCPTCHECK is run in the same environment
as qmail-smtpd (Note that qmail-smtpd changes its CWD to qmail-home
[typically /var/qmail] at startup). Additionally $SENDER is set to the
envelope from (mail from:) and $RECIPIENT is set to the envelope
recipient (for the current rcpt to:). Based on the return code (exit
value) of $RCPTCHECK, the rcpt to: address will either be accepted or
rejected as follows:

- 100: recipient is rejected with "553 sorry, no mailbox here by that
  name. (#5.1.1)"
- 111: connection is dropped with a temporary error "421 unable to
  verify recipient (#4.3.0)"
- 120: connection is dropped with a temporary error "421 unable to
  execute recipient check (#4.3.0)"
- All others: recipient is accepted.

120 is used internally (by the patch) if $RCPTCHECK cannot be executed.

Useful for validating recipient to addresses with an arbitrary program
(such as fastforward in '-n' mode).

Original: qmail-1.03-realrcptto-2006.12.10.patch

The qmail-realrcptto patch copies logic from qmail-send, qmail-lspawn,
qmail-getpw, and qmail-local into qmail-smtpd and qmail-qmtpd, so that
if a local delivery (i.e., one for a domain in /var/qmail/control/locals
or virtualdomains) would eventually bounce due to a missing .qmail file,
then that recipient address is rejected during the SMTP or QMTP protocol
conversation. There are other qmail patches around that do similar jobs
(badrcptto, etc.); the focus of this patch is to get this functionality
with no additional administrative effort, rather than qmail-smtpd's
running speed. You just set up your .qmail files, as you would have to
do anyway, and the rest is automatic, though slower than a CDB lookup.

Addresses which use the default delivery instructions are never rejected
by this patch, because they would never be bounced due to the lack of a
.qmail file.

This patch is less effective when there are .qmail-default files, or
when qmaild does not have sufficient filesystem permissions to stat()
users' .qmail files, since in those cases, qmail-smtpd cannot know that
the delivery would later bounce due to the lack of a .qmail file. For
example, I'm told that this patch is not useful for virtual domains
managed with vpopmail, since an applicable .qmail-default file always
exists. (I'm not familiar with vpopmail myself.) The patch may still be
useful for other local or virtual domains on the same server, if they
are not managed by vpopmail.

- Remove realrcptto references from qmail-qmtpd(8) and qmail-smtpd(8)
- Add qmail-rcptcheck-realrcptto(8) program and manual page
- Adjust realrcptto.c messages for the new context

Note that this leaves qmail-qmtpd(8) without realrcptto functionality.
Porting the RCPTCHECK patch would probably do the trick.

qmail-rcptcheck runs an administrator-defined sequence of programs to
check SMTP envelope senders and recipients. Checks must adhere to the
RCPTCHECK interface. If any check rejects, the message is rejected.

qmail-rcptcheck is most commonly invoked from qmail-smtpd via RCPTCHECK,
but also runs under qmail-spp (not documented here), so if and when we
switch to that, recipient-checking programs won't need to be changed.

- Remove references from qmail-smtpd(8)
- Extract logic to badrcptto.c
- Add qmail-rcptcheck-badrcptto(8) program and manual page