参考配置如下

Here is how i run docker-mailserver as a backup MX.

Create postfix-main.cf in config directory and add the following:

relay_domains = hash:/tmp/docker-mailserver/backupmx/relays
transport_maps = hash:/tmp/docker-mailserver/backupmx/transport
relay_recipient_maps = hash:/tmp/docker-mailserver/backupmx/relay_recipients
maximal_queue_lifetime = 14d

Create a directory called backupmx and the following files relays, transport and relay_recipients.

relays should contain the domains you would like to queue & relay mail for. E.g.

domain1.com OK
domain2.com OK

transport should contain the final destination mail server to relay the queued email to. E.g.

domain1.com smtp:mail.domain1.com
domain2.com smtp:mx1.domain2.com

relay_recipients should contain a list of valid recipients that will be accepted, queued and relayed. E.g.

使用@代表此域名下全部邮箱

@domain1.com OK
@domain2.com OK

For the above to work, the following commands must be run inside the container:

cd /tmp/docker-mailserver/backupmx/
postmap relays
postmap transport
postmap relay_recipients
service postfix restart

参考资料：https://github.com/docker-mailserver/docker-mailserver/issues/254#issuecomment-521184784