Mail.log
Oct 24 22:27:43 mail postfix/smtpd[7662]: connect from my.desk.top.ip
Oct 24 22:27:43 mail postfix/smtpd[7662]: warning: connect to Milter service inet:localhost:8891: Connection refused
Oct 24 22:27:44 mail postfix/smtpd[7662]: NOQUEUE: reject: RCPT from my.desk.top.ip: 554 5.7.1 <receipt@email.com>: Relay access denied; from=<info@problematicdomain.com> to=<receipt@email.com> proto=ESMTP helo=<DESKTOPFTP67QJ>
Oct 24 22:27:46 mail postfix/smtpd[7662]: disconnect from my.desk.top.ip

Oct 24 22:27:12 auth: Debug: passwd-file(info@problematicdomain.com,my.desk.top.ip,<pLSYw1BcsgBeQ1jL>): lookup: user=info@problematicdomain.com file=/etc/dovecot/passwd
Oct 24 22:27:12 auth: Debug: client passdb out: OK  1   user=info@problematicdomain.com
Oct 24 22:27:12 auth: Debug: master in: REQUEST 997982209   7658    1   effa60cd62c34b72950ad17e6f08066c    session_pid=7661
Oct 24 22:27:12 auth: Debug: passwd-file(info@problematicdomain.com,my.desk.top.ip,<pLSYw1BcsgBeQ1jL>): lookup: user=info@problematicdomain.com file=/etc/dovecot/users
Oct 24 22:27:12 auth: Debug: master userdb out: USER    997982209   info@problematicdomain.com  uid=5000    gid=5000    home=/var/spool/vmail/problematicdomain.com/
Oct 24 22:27:12 pop3-login: Info: Login: user=<info@problematicdomain.com>, method=PLAIN, rip=my.desk.top.ip, lip=172.31.1.100, mpid=7661, TLS, session=<pLSYw1BcsgBeQ1jL>
Oct 24 22:27:12 pop3(info@problematicdomain.com): Info: Disconnected: Logged out top=0/0, retr=0/0, del=0/13, size=15495

smtpd_sasl_auth_enable = yes
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

myhostname = mail.servermaindomain.gr
mydestination = mail.servermaindomain.gr, localhost.servermaindomain.gr, localhost
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = $myhostname
mynetworks = 127.0.0.0/8, 10.0.0.0/24
mailbox_size_limit = 0
home_mailbox = Maildir/
virtual_mailbox_domains = /etc/postfix/vhosts
virtual_mailbox_base = /var/spool/vmail
virtual_mailbox_maps = hash:/etc/postfix/vmaps
virtual_minimum_uid = 1000
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000
recipient_delimiter = +
inet_interfaces = all
inet_protocols = ipv4
broken_sasl_auth_clients = yes
#smtpd_sasl_local_domain = $myhostname
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
#smtpd_sasl_path = auth/dovecot
smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
virtual_alias_maps = hash:/etc/postfix/virtual
message_size_limit = 26240000

# DKIM
# --------------------------------------
milter_default_action = accept
milter_protocol = 2
smtpd_milters = inet:localhost:8891
non_smtpd_milters = inet:localhost:8891