Mailman for Plesk - allow use together with delimiter used in postfix main.cf
If you have configured additional delimiters in postfix (/etc/postfix/main.cf) it is not possible to successfully deliver a mail to a mailing list - if that mailing list address contains also one of the symbols configured as delimiter.
The solution is very simple and could be a very generic change in plesk standard config:
In /etc/postfix/master.cf just change the config string for mailman in the end of line from ${nexthop} ${user} ${recipient}
to:
${nexthop} ${mailbox}
This will parse all necessary parameters before the @.
Taken from: http://www.postfix.org/pipe.8.html

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IG