The E-Mail plugin opens a UNIX domain socket and starts accepting connections on that socket. Clients can connect to this socket and submit statistics about email messages. A sample plugin for SpamAssassin can be found in
Use of this plugin is deprecated. If you want to submit statistics to the daemon, for example about email messages, please use the UnixSock plugin instead.
Unfortunately most mail transfer agents (MTAs, also often inaccurately called "mail servers") do not offer an interface to get some statistics out of them. You can, however, use the Tail plugin to get statistics such as "number of rejected mails per second" out of the log files. Other information, such as the current queue length, may be acquired by the FileCount plugin.
<Plugin email> SocketFile "/var/run/collectd-email" SocketGroup "mail" SocketPerms 660 MaxConns 4 </Plugin>
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