Cyrus IMAP is an open source email, contacts and calendar server. It differs from other mail servers in that it is designed to run on sealed systems where users access mail remotely through internet protocols such as (K)POP, NNTP or the eponymous IMAP rather than locally.
First install the AUR package. Afterwards, before starting Cyrus for the first time, you need to initialise the configuration directory and mail partitions. Adjust the default paths in
/etc/cyrus/imapd.conf if desired, then run the mkimap command as user cyrus and group mail:
# runuser -u cyrus -g mail mkimap /etc/cyrus/imapd.conf
To receive messages, you need to configure your mail transfer agent to hand incoming mail directly to Cyrus. The preferred delivery method is through Cyrus's LMTP server, which listens on the socket
/run/cyrus/socket/lmtp by default. For example, to have Postfix deliver mail addressed to virtual mailboxes to Cyrus, add the following line to
virtual_transport = lmtp:unix:/run/cyrus/socket/lmtp