What's up with mail.ru and postfix?

Question

Email

Letters are normally sent everywhere except for mail.ru. They are kind of special. It crashes like this:

May  6 14:00:07 fra1 postfix/master[30688]: terminating on signal 15
May  6 14:00:07 fra1 postfix/master[30868]: daemon started -- version 2.11.0, configuration /etc/postfix
May  6 14:00:30 fra1 postfix/pickup[30871]: 479B5140FD1: uid=33 from=<www-data>
May  6 14:00:30 fra1 postfix/cleanup[30876]: warning: connect to Milter service inet:localhost:8891: Connection refused
May  6 14:00:30 fra1 postfix/cleanup[30876]: 479B5140FD1: message-id=<[email protected]>
May  6 14:00:30 fra1 postfix/qmgr[30872]: 479B5140FD1: from=<[email protected]>, size=1145, nrcpt=1 (queue active)
May  6 14:00:30 fra1 postfix/smtp[30878]: 479B5140FD1: to=<[email protected]>, relay=mxs.mail.ru[217.69.139.150]:25, delay=0.29, delays=0.02/0.01/0.16/0.11, dsn=5.0.0, status=bounced (host mxs.mail.ru[217.69.139.150] said: 550 Unroutable sender address (in reply to MAIL FROM command))
May  6 14:00:30 fra1 postfix/cleanup[30876]: 9D588140FD3: message-id=<[email protected]>
May  6 14:00:30 fra1 postfix/qmgr[30872]: 9D588140FD3: from=<>, size=2922, nrcpt=1 (queue active)
May  6 14:00:30 fra1 postfix/bounce[30879]: 479B5140FD1: sender non-delivery notification: 9D588140FD3
May  6 14:00:30 fra1 postfix/qmgr[30872]: 479B5140FD1: removed
May  6 14:00:30 fra1 postfix/local[30880]: 9D588140FD3: to=<[email protected]>, relay=local, delay=0.02, delays=0/0.01/0/0.01, dsn=2.0.0, status=sent (delivered to mailbox)
May  6 14:00:30 fra1 postfix/qmgr[30872]: 9D588140FD3: removed

Naturally, I googled error 550, where they write a lot about it, but as such a solution cannot be found. What to do with it?
My postfix configs:

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
append_dot_mydomain = no
readme_directory = no
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = fra1
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = fra1, localhost.localdomain, , localhost
relayhost = 
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all
milter_default_action = accept
milter_protocol = 2
smtpd_milters = inet:localhost:8891
non_smtpd_milters = inet:localhost:8891

Answer 1

I put a normal domain in myhostname - it worked. Attention, the question is, what if I have 20 domains on my server?

Answer 2

The problem is that the sender address says "[email protected]" fra1 through external DNS to resolve in what will be?

Answer 3

An old misfortune with mailru, in the headers (I don’t remember which ones) there should not be localhost.
I even specially started a mailbox for myself for testing mail, if it got there, then everything will be ok with the rest of the services.