This is slightly off-topic as it's not about djb, but about qmail. Still: I have some experience with qmail. While I agree that it's generally very nice and ce

This is slightly off-topic as it's not about djb, but about qmail. Still: I have some experience with qmail. While I agree that it's generally very nice and certainly incredibly bug free, that quality comes at a price: Lack of features. The moment you start adding stuff: Server-side filtering (like sieve), LMTP, virus checking, spam filtering, virtual users - all that stuff you need to run a modern mail server - you will have to patch qmail. And by manually patching your installation, you are picking up responsibility: Now that you are not running stock qmail, but something you patched and installed yourself, you will no longer be able to rely on your distribution for security fixes and you'll have to keep updated and repatch yourself. And while qmail is beautiful and bugfree, the same can not always be said for the additional patches, so you WILL be patching. If you get all the patches for the functionality you need to actually play together that is. If qmail solves your issue and you are prepared for this, then go with qmail. If you need a ton of functionality built-into your mailserver, probably go Exim and if you need good compromise between featureset, architecture and security, then you'll probably take postfix.