Where can I find the file syntax doc for postmap in postfix?

Question

linux

We configure /etc/postfix/sender_relay and then postmap /etc/postfix/sender_relay and the sender_relay.db file appears which we include in main.cf
Everything is fine, everything works. But often sender_relay contains configs that are only intuitive and inherited from ready-made instructions. When the situation is not quite standard, you want more freedom, but then I ran into a problem. I couldn't find any explanation on postfix.org about the syntax and functionality of these configs. There, as I understand it, the information is only for files like main.cf
Correct me if I'm wrong, I will be very happy to help, maybe my eyes are just blurry.

Answer 1

man postmap won't save you???
[[email protected] ~]$ rpm -ql postfix | grep man
/usr/share/man/man1/mailq.1.gz
/usr/share/man/man1/mailq.postfix.1.gz
/usr/share/man/man1/newaliases.1.gz
/usr/share /man/man1/newaliases.postfix.1.gz
/usr/share/man/man1/postalias.1.gz
/usr/share/man/man1/postcat.1.gz
/usr/share/man/man1/postconf .1.gz
/usr/share/man/man1/postdrop.1.gz
/usr/share/man/man1/postfix.1.gz
/usr/share/man/man1/postkick.1.gz
/usr/share /man/man1/postlock.1.gz
/usr/share/man/man1/postlog.1.gz
/usr/share/man/man1/postmap.1.gz
/usr/share/man/man1/postmulti.1 .gz
/usr/share/man/man1/postqueue.1.gz
/usr/share/man/man1/postsuper.1.gz
/usr/share/man/man1/sendmail.postfix.1.gz
/usr/share/man/man1/smtp-sink.1.gz
/usr/share /man/man1/smtp-source.1.gz
/usr/share/man/man5/access.5.gz
/usr/share/man/man5/aliases.5.gz
/usr/share/man/man5/aliases .postfix.5.gz
/usr/share/man/man5/body_checks.5.gz
/usr/share/man/man5/bounce.5.gz
/usr/share/man/man5/canonical.5.gz
/usr /share/man/man5/cidr_table.5.gz
/usr/share/man/man5/generic.5.gz
/usr/share/man/man5/header_checks.5.gz
/usr/share/man/man5/ldap_table .5.gz
/usr/share/man/man5/master.5.gz
/usr/share/man/man5/memcache_table.5.gz
/usr/share/man/man5/mysql_table.5.gz
/usr/share/man/man5/nisplus_table.5.gz
/usr/share/man/man5/pcre_table.5.gz
/usr/share/man/man5/pgsql_table.5.gz
/usr/share/man/man5 /postconf.5.gz
/usr/share/man/man5/postfix-wrapper.5.gz
/usr/share/man/man5/regexp_table.5.gz
/usr/share/man/man5/relocated.5.gz
/usr/share/man/man5/sqlite_table.5.gz
/usr/share/man/man5/tcp_table.5.gz
/usr/share/man/man5/transport.5.gz
/usr/share/man/man5 /virtual.5.gz
/usr/share/man/man8/anvil.8.gz
/usr/share/man/man8/bounce.8.gz
/usr/share/man/man8/cleanup.8.gz
/usr /share/man/man8/defer.8.gz
/usr/share/man/man8/discard.8.gz
/usr/share/man/man8/dnsblog.8.gz
/usr/share/man/man8/error .8.gz
/usr/share/man/man8/flush.8.gz
/usr/share/man/man8/lmtp.8.gz
/usr/share/man/man8/local.8.gz
/usr/share/man/man8 /master.8.gz
/usr/share/man/man8/oqmgr.8.gz
/usr/share/man/man8/pickup.8.gz
/usr/share/man/man8/pipe.8.gz
/usr /share/man/man8/postscreen.8.gz
/usr/share/man/man8/proxymap.8.gz
/usr/share/man/man8/qmgr.8.gz
/usr/share/man/man8/qmqpd .8.gz
/usr/share/man/man8/scache.8.gz
/usr/share/man/man8/sendmail.8.gz
/usr/share/man/man8/showq.8.gz
/usr/share /man/man8/smtp.8.gz
/usr/share/man/man8/smtpd.8.gz
/usr/share/man/man8/spawn.8.gz
/usr/share/man/man8/tlsmgr.8 .gz
/usr/share/man/man8/tlsproxy.8.gz
/usr/share/man/man8/trace.8.gz
/usr/share/man/man8/trivial-rewrite.8.gz
/usr/share/man/man8/verify.8.gz
/usr/share/man /man8/virtual.8.gz