25 years of Postfix

Qmail also tended to make itself unpopular by trying to deliver n messages to the same remote MTA in parallel using n SMTP connections, rather than sequentially across the same SMTP connection.

Like maildirs, VERP support and flexible forwarding and aliasing were among the qmail features that the other big MTAs took on board fairly rapidly. (VERP – which may really have been an ezmlm, rather than qmail, thing – is a bit of a two-edged sword; while it is useful for processing bounces, without it, if you have a big mailing list with 100 recipients on the same remote site, you could send 100 RCPT TO commands and then one copy of the body, but with it, you would have to send 100 separate copies of the same message each with a different MAIL FROM. Of course, these days, sending the same message to 100 recipients on the same remote site would probably get you into trouble as a prospective spammer, but that's a different story.)

Qmail did have its share of clever ideas, but it was missing important features – or in any case features that the rest of the MTA community considered important but that DJB didn't agree with, or that only rose to importance after DJB was mostly done with qmail development – and implementations of these for qmail, if they existed, were often a hassle to find and add. In later years there used to be curated collections of patches one would need to apply to make qmail actually usable, and by now there are semi-official beefed-up releases of public-domain qmail, but the MTA caravan has moved on and these are mostly of interest to die-hard qmail devotees.