Normally, sendmail limits the number of outbound RCPT TO: commands allowed per session to the size of the DEFAULT_MAX_RCPT compile-time macro (MAX...), which is defined as 100 in sendmail/conf.c. When delivering an envelope, sendmail will deliver only the maximum number of recipients on the first try. Any that are left over will be deferred until a later delivery attempt (usually during the same queue run).

One problem with piling many recipients into a single envelope is that some sites on the Internet refuse to accept mail when the envelope contains too many recipients. Another, but opposite, problem is that some sites can accept more than 100 recipients per envelope, and you would prefer to send them as many as they can handle in a single transaction.

One way to limit or expand the number of recipients allowed in an envelope is to use this r= delivery agent equate:

r=val

If val is set to a non-zero value, it changes the limit on the number of recipients allowed to the value specified. If val is less than or equal to zero, the limit is set to the value of the DEFAULT_MAX_RCPT compile-time macro (MAX...).

Some delivery agents provide mc macros with which to add an r= equate. For example, the following mc configuration lines add that default to the various smtp delivery agents:

define(`SMTP_MAILER_MAXRCPTS', `80') this must be
MAILER(`smtp')                       before this

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

For some delivery agents, there are no mc configuration macros available to directly give a value to this r= equate. Instead, you can use a bit of sleight of hand to add an r= to a particular delivery agent:

define(`LOCAL_MAILER_PATH', `/usr/lib/mail.local, r=200') this must be
MAILER(`local')                                           before this

The LOCAL_MAILER_PATH mc configuration macro (See this section) is usually used to define the path for the local delivery agent. Instead of using it for that reason, here we simply restate the path that appears in the current sendmail.cf file, and add the r= declaration to that path. As with all modifications of delivery agent equates, the modification must precede the MAILER declaration for the corresponding delivery agent.