In the current implementation, sieves autoresponder is using an empty sender address for auto reply.

We suggest the following config change:

/etc/dovecot/conf.d/90-plesk-sieve.conf

plugin {
  sieve = ~/.dovecot.sieve
  sieve_dir = ~/sieve

  # Horde webmail (Ingo sieve backend) is not aware of RFC 'imap4flags' and
  # 'enotify' extensions. Enable old deprecated ones.
  sieve_extensions = +notify +imapflags

  sieve_vacation_send_from_recipient = "yes"   # <- New
}

This setting ensure that the original recipient is used as envelope sender address for the auto reply, especially required for big providers like google and microsoft. This setting also enables DKIM signing for auto responder to be compliant with SPF / DKIM and DMARC policies.