qmail

Tn the last couple of weeks my qmail server was under heavy traffic that rendered it mostly inaccessible.
the facts
what hapened was that too many smtp sessions were opened sending too many messages to non-existing accounts, we're talking here about 512 incoming smtp connection, over 6000 mails in the queue and over 256 outgoing smtp connection, and if that is not enough over 60 concurrent local deliveris.
the analysis

I have been using qmail for 6 month now on a server hosting over 30 domains - one of them is an ISP - so i think that now i can say something usefull.
i can't argue about qmail's code or performance, it can take whatever you throw at it and it is being used by google's mail already.
qmail is just 3 parts of a big system, it offers only smtp, pop and delivery agent. you still need imap, mailing list, webmail app and probably a DB backend for storing users. all that can be done easily but with a significant amount of work to get everything to work together nicely.

According to Wikipedia Greylisting is a simple method of defending electronic mail users against e-mail spam. In short, a mail transfer agent which uses greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again to send it later, at which time the destination will accept it. If the mail is from a spammer, it will probably not be retried, and spam sources which re-transmit later are more likely to be listed in DNSBLs and distributed signature systems such as Vipul's Razor.

OK maybe my history with qmail doesn't go a long way (just 3 month) but i guess i got a hold of it
I'm already running a mail server with 30+ domains and 3000+ mailboxes

what i want to do in this series of posts is talk about setting up a qmail server to host multiple domains, while there is a pretty good guide at www.qmailrocks.org i will not go into a lot of details, but rather explain things that i could not really get from qmailrocks.

introduction: