I have a couple of vpopmail/qmail-based e-mail servers that have worked well
for many years.
A few years ago, we began using the Calendar Server on MacOSX. The calendar
server sits on an internet pipe which doesn't pass port 25, so I can't use the
built-in mail server to handle calendar invites and replies. Luckily, the
Calendar Server configuration allows you to set up an e-mail address which it
will use to send invites via SMTP and receive replies to the invites via IMAP.
Initially, I tried to set up an address on one of my vpopmail/qmail servers, as
they service the domains which these calendar servers sit on. However, the
Calendar Server uses "+" subaddressing, and vpopmail/qmail use "-"
The qmail docs say that you can configure the subaddress separator character by
changing the "-" to a "+" following the user name in /var/qmail/users/assign.
In vpopmail, users aren't in the assign file - it seems to contain a listing of
domains that vpopmail services. Unsurprisingly, changing the "-" to a "+" and
running qmail-newu as the qmail docs suggest doesn't change the subaddressing
behavior for that domain.
The workaround since I did this research last has been to use a Gmail account
specifically for each Calendar Server I maintained. This worked for a while,
but then at some point recently, Gmail and Google Calendar started causing
invites to be handled improperly. I'm not sure what conditions are necessary,
but it seems like it has something to do with the recipient using Google
Calendar instead of another calendar service with their Gmail address (and why
In any case, I'm again looking into how to make a domain on one of my
vpopmail/qmail servers use the "+" separator for subaddresses, rather than "-",
and I'm coming up dry. I realize that changing the subaddress separator will
have an effect on ezmlm-idx, which I use on this server, so that's why I only
want to change the subaddress separator on a single domain.