Use lmtp instead of lda for delivery.

roles/mailserver/files/etc_postfix_master.cf

 dspam     unix  -       n       n       -       10      pipe
   flags=Ru user=dspam argv=/usr/bin/dspam --deliver=innocent,spam --user ${user}@${domain} -i -f $sender -- $recipient
 dovecot   unix  -       n       n       -       -       pipe
-  flags=DRhu user=vmail:vmail argv=/usr/lib/dovecot/dovecot-lda -f ${sender} -d ${user}@${nexthop}
+  flags=DRhu user=vmail:vmail argv=/usr/lib/dovecot/lmtp -f ${sender} -d ${user}@${nexthop}

roles/mailserver/templates/etc_postfix_main.cf.j2

 inet_interfaces = all
 
 # dovecot db
-virtual_transport = dovecot
+virtual_transport = lmtp:unix:private/dovecot-lmtp
+mailbox_transport = lmtp:unix:private/dovecot-lmtp
+
 dovecot_destination_recipient_limit = 1
 virtual_mailbox_domains = pgsql:/etc/postfix/pgsql-virtual-mailbox-domains.cf
 virtual_mailbox_maps = pgsql:/etc/postfix/pgsql-virtual-mailbox-maps.cf