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+Postfix default configuration can easily be overrided providing a `config/postfix-main.cf` at postfix format.
+This can be used to also add configuration that are not in out default configuration.
+
+Each line in the provided line will be loaded into postfix.
+
+Have a look to the code for more information: 
+https://github.com/tomav/docker-mailserver/blob/master/target/start-mailserver.sh#L196-L206
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