Some useful links to explain the concepts of Postfix
- http://blog.schaal-24.de/mail/postscreen-im-kampf-gegen-spam/?lang=en
- https://www.howtoforge.com/hardening-postfix-for-ispconfig-3
- https://workaround.org/ispmail/squeeze/postfix-domain-types
- https://workaround.org/article/postfix-database-configuration
- https://www.howtoforge.com/virtual_postfix_antispam
- https://rtcamp.com/tutorials/mail/
- https://www.linode.com/docs/email
- https://www.linode.com/docs/email/running-a-mail-server
- http://www.postfix.org/QSHAPE_README.html
- https://easyengine.io/tutorials/mail/postfix-queue/
- http://wiki.zimbra.com/wiki/Managing_The_Postfix_Queues
- http://www.tullyrankin.com/managing-the-postfix-queue
- https://www.wirehive.net/blog/2014/11/07/5-top-tips-for-reviewing-your-postfix-mail-queue
- Sorting queued mails by From address
sudo mailq | awk '/^[0-9,A-F]/ {print $7}' | sort | uniq -c | sort -n- Holding queued mails by From address
sudo mailq| grep '^[A-Z0-9]'| grep <sender-ID>| cut -f1 -d' ' | tr -d \*|sudo postsuper -h -- Holding queued mails by To address
sudo mailq | tail -n +2 | grep -v '^ *(' | awk 'BEGIN { RS = "" } { if ($8 == "<recipient>") print $1 } ' | tr -d '*!' | sudo postsuper -h -- Holding queued mails by Domain
sudo mailq| grep '^[A-Z0-9]'| grep @<domain>| cut -f1 -d' ' | tr -d \*|sudo postsuper -h -- Holding emails from the [active|deferred] queue based on subject
sudo find /var/spool/postfix/[active|deferred]/ -type f -exec grep -il '<subject>' '{}' \; | xargs -n1 basename | sudo postsuper -h -- Removing Mails based on sender Address
sudo mailq| grep '^[A-Z0-9]'| grep <sender-ID>| cut -f1 -d' ' | tr -d \*|sudo postsuper -d -- Removing Mails based on Domain
sudo mailq| grep '^[A-Z0-9]'| grep @<domain>| cut -f1 -d' ' | tr -d \*|sudo postsuper -d -- Delete mails to a specific mail address
sudo mailq | tail -n +2 | grep -v '^ *(' | awk 'BEGIN { RS = "" } { if ($8 == "<recipient-ID>") print $1 } ' | tr -d '*!' | sudo postsuper -h -