The postfix tag is described as being for the mailer; however, a number of folks use it when describing issues with infix and postfix notation.
As far as I can tell, there are very few postfix-notation questions as compared to postfix-mailer. I suggest we first retag all postfix-notation questions as such, and then rename/merge postfix to postfix-mailer.
I've already started on some retagging.
Update: Finished retagging those posts. Now onwards with:
The following searches cannot be blanket-retagged, look carefully:
That ought to cover all of the mistagged questions.