Altering message timeouts

After sitting in the queue for a few days, a message will time out. This is to insure that at least the sender is aware of the inability to send a message. The timeout is typically set to five days. It is sometimes considered convenient to also send a warning message if the message is in the queue longer than a few hours (assuming you normally have good connectivity; if your messages normally took several hours to send you wouldn't want to do this because it wouldn't be an unusual event). These timeouts are set using the Timeout.queuereturn and Timeout.queuewarn options in the configuration file (previously both were set using the T option).

If the message is submitted using the NOTIFY SMTP extension, warning messages will only be sent if NOTIFY=DELAY is specified. The queuereturn and queuewarn timeouts can be further qualified with a tag based on the Precedence: field in the message; they must be one of "urgent" (indicating a positive non-zero precedence) "normal" (indicating a zero precedence), or "non-urgent" (indicating negative precedences). For example, setting "Timeout.queuewarn.urgent=1h" sets the warning timeout for urgent messages only to one hour. The default if no precedence is indicated is to set the timeout for all precedences. The value "now" can be used for -O Timeout.queuereturn to return entries immediately during a queue run, (for example, to bounce messages independent of their time in the queue.

Since these options are global, and since you cannot know how long another host outside your domain will be down, a five day timeout is recommended. This allows a recipient to fix the problem even if it occurs at the beginning of a long weekend. RFC 1123 section 5.3.1.1 says that this parameter should be ``at least 4-5 days''.

The Timeout.queuewarn value can be piggybacked on the T option by indicating a time after which a warning message should be sent; the two timeouts are separated by a slash. For example, the line:

   OT5d/4h