On 23 Nov 2020, at 06:49, maciejm <na...@mandzur.pl> wrote: > "RFC 822 Message-ID is not required"
RFC 822 has been obsoleted several times. RFC 5322 states: Though listed as optional in the table in section 3.6, every message SHOULD have a "Message-ID:" field. Furthermore, reply messages SHOULD have "In-Reply-To:" and "References:" fields as appropriate and as described below. And: RFC 2119 SHOULD This word, or the adjective "RECOMMENDED", mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course. So SHOULD is much stronger than "it's a good idea" and much more like "You better have a really good reason for ignoring this". I would feel comfortable rejecting messages without a Message-ID. -- Imagine all the people Sharing all the world