BDAT to DATA translation on submission service when checkpassword is involved

[Dan Conway]

Hello,

I'm having issues with Dovecot translating "BDAT" commands (CHUNKING) 
into "DATA" commands when the backend does not support it in the 
submission service. I use "checkpassword" to authenticate users and 
judging by older mailing list entries the presence of "submission_*" 
directives must be in place for Dovecot to translate. Even with these 
directives set, the translation doesn't seem to occur.

checkpassword returns "director_tag=remote_smtp" (along with other 
fields such as nopassword=y proxy=y) which in turn sets the backend host 
to relay the connection to. I have a feeling the use of checkpassword 
has something to do with this lack of translation.

If the "submission_*" directives must be in place for this translation 
to occur, which ones are they? Can I return these fields from checkpassword?


Output of doveconf -n:

# 2.3.15 (0503334ab1): /etc/dovecot/dovecot.conf
# OS: Linux 4.15.0-147-generic x86_64 Ubuntu 18.04.5 LTS
# Hostname: xyz
auth_debug = yes
auth_debug_passwords = yes
auth_mechanisms = plain login
auth_verbose = yes
director_mail_servers = x.x.x.x at remote_smtp
director_servers = x.x.x.x
disable_plaintext_auth = no
mail_log_prefix = "%Us(%u) [%r]: "
passdb {
   args = /usr/local/bin/checkpassword
   driver = checkpassword
}
protocols = " imap pop3 submission"
service anvil {
   client_limit = 3553
}
service auth {
   client_limit = 3550
}
service director {
   fifo_listener login/proxy-notify {
     mode = 0600
     user = $default_login_user
   }
   inet_listener {
     address = x.x.x.x
     port = 9090
   }
   unix_listener director-admin {
     mode = 0600
   }
   unix_listener login/director {
     mode = 0666
   }
}
service imap-login {
   executable = imap-login director
   inet_listener imap {
     address = x.x.x.x
     port = 143
   }
   inet_listener imaps {
     address = x.x.x.x
     port = 993
     ssl = yes
   }
   process_limit = 1000
   process_min_avail = 0
   service_count = 1
}
service imap {
   process_limit = 2048
   process_min_avail = 0
   service_count = 1
   vsz_limit = 384 M
}
service pop3-login {
   executable = pop3-login director
   inet_listener pop3 {
     address = x.x.x.x
     port = 110
   }
   inet_listener pop3s {
     address = x.x.x.x
     port = 995
     ssl = yes
   }
   process_limit = 450
}
service pop3 {
   process_limit = 190
   process_min_avail = 0
   service_count = 1
}
service submission-login {
   executable = submission-login director
   inet_listener smtp {
     address = x.x.x.x
     port = 25
   }
   inet_listener smtps {
     address = x.x.x.x
     port = 465
     ssl = yes
   }
   inet_listener submission {
     address = x.x.x.x
     port = 587
   }
   process_limit = 2000
}
ssl_cert = </etc/...
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
ssl_min_protocol = TLSv1.1
submission_backend_capabilities =
submission_host = x.x.x.x
submission_relay_host = x.x.x.x
submission_relay_port = 465
submission_relay_ssl = smtps
submission_relay_trusted = yes
userdb {
   args = /etc/dovecot/userdb.conf
   driver = ldap
}
protocol imap {
   imap_logout_format = bytes=%i/%o, del=%e
   mail_max_userip_connections = 20
}
protocol pop3 {
   mail_max_userip_connections = 20
   pop3_logout_format = top=%t/%p, retr=%r/%b, del=%d/%m, size=%s
}
protocol submission {
   mail_max_userip_connections = 10
}
local_name *.domain.com {
   ssl_cert = </etc/...
   ssl_key = # hidden, use -P to show it
}