Have a look at this recent discussion:

http://dovecot.2317879.n4.nabble.com/SMTPUTF8-support-td67266.html


Am 09.05.2019 um 22:15 schrieb Jerry via dovecot <dovecot@dovecot.org>:

I am trying to find out if Dovecot supports "smtputf8". Obviously, I
am looking in the wrong places, but I just cannot find a definitive
answer.

Thanks!

--
Jerry