At small sites, where mail messages are rarely queued, the time interval chosen can
be small to ensure that all mail is delivered promptly. An interval of 15m (15 minutes)
might be appropriate.
At many sites, an interval of one hour is probably best. It is short enough to ensure
that delays in delivery remain tolerable, yet long enough to ensure that queue processing
does not overlap (see ?§11.8.3 on page 434 for a way to run a persistent queue
runner that avoids overlapping runs).
At large sites with huge amounts of mail and at sites that send a great deal of international
mail, the interval has to be carefully tuned by observing how long it takes sendmail
to process its queues and what causes that process to take a long time. Points to
consider are the following:
??? Network delays or delays at the receiving host can cause delivery to that host to
time out. Timeouts are set withth e Timeout option (?§24.9.119 on page 1097).*
Each such timeout is logged at LOG_NOTICE with a message such as this:
timeout waiting for input from host during what
Here, host is the name of the other host, and what specifies which timeout triggered
the message (such as ???client HELO??? for to_helo). In general, timeouts
Table 11-5. Meaning of time letters
Letter Meaning
w Week
d Day
h Hour
m Minute
s Second
* Note that prior to V8 sendmail, the r option set one timeout for all SMTP timeouts.
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