Queue groups and the Q= delivery agent equate were introduced in V8.12 sendmail. In Section 11.4 we show you how to declare and use queue groups. For example, the following mc configuration line declares a queue group named slowmail, in which we plan to defer SMTP mail:

QUEUE_GROUP(`slowmail', `P=/var/spool/mqueue/slowqueue')

Here, the P= queue group equate says that the queue for the slowmail queue group will be /var/spool/mqueue/slowqueue.

The Q= delivery agent equate associates a delivery agent with a queue group. For the smtp delivery agent, for example, the following delivery agent equate will cause its queue directory to become /var/spool/mqueue/slowqueue because of the previous queue group declaration:

Q=slowmail

Several mc configuration macros are available with which to declare queue groups for selected delivery agents. For example, the following defines the slowmail queue group, and associates the smtp delivery agent with it:

QUEUE_GROUP(`slowmail', `P=/var/spool/mqueue/slowqueue')
define(`SMTP_MAILER_QGRP', `slowmail')
MAILER(`smtp')                                must follow the above two

Whenever you assign a queue group to a delivery agent, the use of a macro that ends in _MAILER_QGRP must precede the MAILER declaration for that delivery agent.

See the section describing a particular delivery agent to find an appropriate mc macro with which to redefine the Q= for that delivery agent. See Table 20-1, in Section 20.4, for a guide to all delivery agents.