You control here how mail is sent and received.
You can restrict the maximum size of message received.
This feature is intended for people without continuous Internet connectivity. This tells sendmail to save the mail without further checking. Later on, one can trigger the delivery of the messages. This is usually done by specifying a post connection command (see Linuxconf ppp dialout support) like "/usr/sbin/sendmail -q". This forces sendmail to process its queue and deliver the messages.
In many cases, you may prefer to set the mail gateway protocol to expensive ESMTP, which queue outgoing mail, but process local ones.
Once in a while sendmail wakes up and tries to deliver email that it was unable to deliver previously. You can see the content of the queue with the command "mailq" (without arguments).
People without continuous Internet connectivity may want to play here. Setting the delay to 0 disable the feature. If your connectivity is on demand, you may want to put a larger number, such as 30 minutes. Then when sendmail will wakes up, it will/should trigger a connection.
Those who disable the feature may want to control sendmail manually (or with a cron job) with the command:
User are allowed to encode some processing in their .forward file.
The processing is done with the bourne shell (/bin/sh). Using
this feature, processing is done with a restricted shell. This shell
only execute commands found in the
A message may encode several recipient and you may want to restrict the maximum number.
Sendmail makes heavy use of the DNS. Machines with no Internet connectivity at all (even behind a firewall) may want to deactivate DNS usage.
On the other end, machines with normal DNS connectivity should force DNS usage.