Sendmail support of empty group addresses (AKA list syntax)

Question

E-mail group addresses such as undisclosed-recipients:; or a group:<u1@example.net>,<u@x.example.net>; are valid forms of addressing according to RFC 5322, see for instance the illustrative example in Appendix A.1.3. In Sendmail, this is called "list syntax". Minimal working example (for Bash):

echo "Date: $(date --rfc-2822)
From: <someone@example.net>
To: a group:<r1@example.net>,<r2@example.net>;
" | sendmail -t

However, trying to submit messages with empty groups leads to error List:; syntax illegal for recipient addresses. Minimal example:

echo "Date: $(date --rfc-2822)
From: <someone@example.net>
To: undisclosed-recipients:;
Bcc: someone-else@example.net
" | sendmail -t

returns

undisclosed-recipients:;... List:; syntax illegal for recipient addresses

How can Sendmail be configured to support empty RFC 5322 group addresses when submitting messages via sendmail -t?

@AndrzejA.Filip I could, it's just not the question here. Moreover, `sendmail -t` is the default for PHP mail() e.g. on *nix systems. — xebeche, Dec 16 '15 at 22:28
How would you like `sendmail -t ...` to process such addresses? a) ignore b) expand LOCAL mailing lists/aliases — AnFi, Dec 18 '15 at 11:12
If I am not mistaken `foo:;` is an empty group. It should be ignored just like `(foo)` or `" "`. — xebeche, Dec 18 '15 at 12:26

score 0 · Accepted Answer · answered Feb 19 '16 at 10:17

After looking at Sendmail's source code my conclusion is that in order to have Sendmail support (or rather ignore) empty groups properly a change of the source code is required.

Empty group addresses such as To: foo:; should simply be ignored just like To: (foo) or To: or '' (i.e. nothing). By debugging I found that this is not an issue with submit.cf. Cf rules are never applied to empty addresses. In parseaddr.c, parseaddr->prescan returns NULL for empty addresses, but not for :;. This can be shown by submitting messages to sendmail -t -d20.1.

Workarounds are:

Use (foo) instead of foo:;
Use "impudent"(*) rewriting + discarding as shown by user at in phpBB: List:; syntax illegal for recipient addresses (archived at https://archive.is/rQJ8X) (code not tested)

(*) quoting the original author

Sendmail support of empty group addresses (AKA list syntax)

1 Answers1