On 8 Jul 2021, at 10:51 pm, John Levine <johnl(_at_)taugh(_dot_)com> wrote:
Maybe we should request two, one for SMTP and one for SUBMIT.
I asked one of the draft's authors if he knows why POP and IMAP have ALPNs
and SMTP doesn't.
I do worry about getting the ALPNs right in the common case that the same host
offers SMTP, SUBMIT, POP, and IMAP.
It is not uncommon for SOHO domains to relay outbound mail via a
provider submission server.
Some care may be needed to make sure that MTAs acting as submission
clients know to use the right ALPN for "SUBMIT". This means that
MTAs should avoid defaulting the ALPN to "SMTP" on ports other than
25, likely sending no "ALPN" unless configured explicitly by the
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