Linux – Display number of messages in linux mail queue

You have RabbitMQ and ZeroMQ, but afaik ZeroMQ doesn't store unprocessed messages in case of a crash. They're both open source and use AMQP, an open messaging protocol.

The messages that have been sent or are trying to be sent are stored in /var/spool/mqueue. Messages that Sendmail has not tried to queue yet can be found in /var/spool/mqueue-client.

So try this (I assume you want to get rid of all messages in the queue):

• Stop sendmail
• rm /var/spool/mqueue/*
• If you want to remove messages in waiting, rm /var/spool/mqueue-client/*.
• Start sendmail

This will clear our your queue folder(s) until the system receives another message. You can double check by running mailq (both queue folders), or sendmail -bp (only the queue folder).

NOTE: With most Linux distributions you can start/stop services with with service sendmail <start|stop|restart> or /etc/init.d/sendmail <start|stop|restart>. Both options have many other status flags which can be observed by typing in the command and service without the status flags.