It appears that Erich Veyhl <ewv.sys.pml@moosecove.org> said:
Shell accounts that hosted procmail used to be routine. Can anyone recommend a reliable host (preferably US) with a shell account or vps that allows procmail processing with sendmail prior to pop retrieval? Sales departments no longer seem to know what that even means.
I think you're unlikely to find anyone who will still let you run your own scripts on their mail server. It's easy enough to set up Postscript on your own VPS but then you have to do all your own spam filtering and deal with the often poor sending reputation of VPS networks. How about a slightly modified VPS approach, pick whatever mail operator you want, run fetchmail on your VPS to collect the mail from their server to your VPS and run procmail there. If you want to handle your own POP or IMAP clients, running your own copy of dovecot is very easy and doesn't have the reputation issues since nobody but you has access to it.