Ranked in these QuestionsQuestion Ranking
Over the years procmail has only had 3 vulnerabilities found and it still does what is was inteded for. As such it is considered by many to be a "finished" product that does not require any more maintenance. It is still packaged in many major distributions.
Pro Easy to use, robust filtering system
Procmail uses Extended Global Regular Expressions Print (egrep) that allows for advanced recipes.
Pro Widely used
Procmail has over the years gathered a loyal following that still provides support and examples.
Pro [delete me]
Con Not maintained
Although still stable, development of procmail has stopped.
Con Archaic syntax
Procmail syntax can be intimidating and lack of cohesive documentation may turn off a lot of people.
Con Natively supports only mbox
Latest version supports maildir by specifying delivery path ending with a /.