allow suffix after a mail address for RFC 3461

[my-name-is-already-taken]

This change makes it possible to Append a DSN specification behind the MAIL and RCPT mail addresses in the smtp protocol.

Currently, curl checks if these addresses start with a '<' or end with a '>' and remove these characters, before adding them when issuing the actual command. So when setting CURLOPT_MAIL_RCPT to <foo@bar.com> NOTIFY=FAILURE, the actual address sent to the server becomes <foo@bar.com> NOTIFY=FAILURE>.

This proposal changes the behavior in the following way: If the address starts with a '<' character, we search the address for the last '>' instead of only checking the last character. Everything that comes behind this bracket is then kept as a suffix in the address.

See also #8232.

[testclutch]

Analysis of PR #16643 at fafb6ae0:

Test 1515 failed, which has NOT been flaky recently, so there could be a real issue in this PR.

Generated by Testclutch

[bagder]

This looks like a good idea to support. I would just like to ask for a little more here:

• documentation - this needs to be described
• a test case or two that verify that this behavior works as intended and documented

[my-name-is-already-taken]

I have fixed an error and added a testcase as well as some documentation.

I had difficulties writing the test, so I would appreciate it if someone checked whether I've done it correcty.

Please let me know if something else is missing.

[vszakats]

Spellcheck says:

Misspelled words:
<htmlcontent> docs/libcurl/opts/CURLOPT_MAIL_RCPT.md: html>body>p
--------------------------------------------------------------------------------
DSN
--------------------------------------------------------------------------------

This should silence it:

--- i/.github/scripts/spellcheck.words
+++ w/.github/scripts/spellcheck.words
@@ -203,6 +203,7 @@ DoT
 doxygen
 drftpd
 dsa
+DSN
 Dudka
 Dymond
 dynbuf

Thanks, all fixed from my end. Can't comment much on the protocol side.

[bagder]

This branch has conflicts that must be resolved

[bagder]

Needs merge conflicts resolved

[my-name-is-already-taken]

I have resolved the conflict and renamed test3211 to test3215.

[vszakats]

LGTM

[bagder]

Thanks!