At my first ISP job, I eventually started using mh for mail. It was based on an awesome concept of sorting everything into directories and having procmail and various helpers to pre-process, including upon receipt and reading. I remember little of the details, but it was truly for the gung-ho neckbeard crowd, and it was well-suited for processing "large amounts" of mail (1993 style). I think MMDF was the MTA trying to do similar things in that vein. Meanwhile my boss was in love with PINE...

Of course, working at an ISP I could also telnet to our NNTP server and read Usenet on the local filesystem. Ugh.