ScanMailX which is a hosted antispam and antivirus company based in Denmark is also using qpsmtpd with great results. The performance is great and the API allow us to add new filters and methods as we need. Jesper Knudsen, 2011/07/11

It's used by the SpamAssassin team as the MTA for their spamtrap infrastructure

It's used on apache.org, perl.org, cpan.org, lists.mysql.org, sourceware.org (aka gcc.gnu.org, cygwin.com)

Qpsmtpd is part of http://roskaposti.net service, which provides email filtering service to over 11 000 clients so far harri_nyman 2006/12/27

qpsmtpd is included as the standard SMTP daemon in the latest version of the SME server distribution. charlie_brady 2006/02/14 01:27

I'm co-owner of a small ISP with ~200 domains, a longtime user (and parttime developer) and very satisfied with qpsmtpd. I have also some commercial customers who are interested in the flexibility of qpsmtpd and will probably order their own qpsmtpd server from me. michael_holzt 2006/02/10 21:34

Am using it on nsa.co.il with ~300 active domains, the BEST thing thats happened to me in a long time in the world of unix based mail systems! — skaag 2006/02/08 02:24

I do, on a three-user vanity-domain site. — tyskjohan 2006/02/07 10:47

I use qpsmtpd as Mail Gateway. — budi_ang 2006/02/08 05:49

I use qpsmtpd for my domain (robinbowes.com) and also for my clients. One of them has 356 domains on an old AMD Duron system which was being brought to its knees by spam - load average was running at around 5. They were using qmail-smtpd with virus and spam scanning running from qmail-queue. I replaced this with qpsmtpd and various plugins (including my own check_validrcptto_cdb) and the server is now ticking along nicely with a load average < 0.5. — robinbowes 2006/02/23 00:13

I use Qpsmtpd on my production server to reject spam and viruses for over 100 domains, and have a few small applications written with the plugin architecture. — fredmoyer 2006/2/25 19:43

I use qpsmtpd on a couple of rather different sites: My own mail server with one user, the mail server of a local Linux user group (few users, but a couple of majordomo mailinglists) and my employer's mail server, which serves a few hundred users in about two dozen domains. I wrote custom plugins for each of them. — hjp 2006/03/03 19:33

I am a big fan of Qpsmtpd and I have integrated it with Qmail which is already running. I run Qpsmtpd on Port 25 and Qmail on Port 2020 and all mail gets filtered with qpsmtpd+dnsbl+spamassassin and then injected into qmail for delivery and this solution rocks.Keep on doing the good work guys and all the best. — Dillip - 2006/05/18 17:16

I'm using qpsmtpd for my private email domains. I had massive problems with spam emails before I installed qpsmtpd in front of my exim smtpd - which now runs in the back-ground and is not reacheable from outside anymore. It was really easy to set-up qpsmtpd; and it works like a charm :) I also wrote some plug-ins which you can download from my CPAN pages. marc 2006/06/27, updated 2007/01/20

I'm using qpsmtpd on two private mail relays hosted on cheap virtual private servers (10$/month). These servers relay the mail through a VPN to a private server running qmail-smtpd that stores the messages in Maildir format. gfk 2006/09/27 16:16

I am just setting up qpsmtpd. I need to write a plugin and I expect to add some documentation here. The only way to generate a new page seems to be to add a link somewhere and this seemed like the logical spot. — gh 2006/12.14

I use qpsmtpd as an email gateway and anti-spam tool. — jamtur01 2007/01/09 07:16

Yes, I am using qpsmtpd for years, it is very good ! And I made an plugins, check_validusers, for checking the valid emails, when the spam rcpt_to wrong email address then it will reject disconnected so it can save many bandwidths friendship updated: 2007/03/18

zootzone.com, a DNS, web and email hosting company, uses qpsmtpd, together with qmail, DSPAM and ClamAv for an incredibly stable, efficient and powerful setup. Replacing qmail-smtpd with qpsmtpd dramatically reduced our spam delivery volume. qpsmtpd's plugin architecture is incredibly powerful, enabling us to integrate it with our infrastructure with ease. zoot 2009/05/26 11:45