MM checks for new mail automatically during a session. You can also tell it to do so at any point. You don't need to know anything in this section unless you are trying to solve problems.
New mail is received into a system directory, typically /usr/spool/mail. In that directory is a file "owned" by each user, named for the user id. For example, the mail for jb51 is collected in the file /usr/spool/mail/jb51. Access to that file is read-write by the owner, jb51, so no one else can see his mail. The spool file is defined by the MM variable incoming-mail, which you should not change unless you make other changes in the way the host handles your mail.
Normally, when you start MM, it checks the spool file and copies any messages there into your mbox. To be more precise, MM does a get command automatically, and then starts checking the spool for new mail at regular intervals. When it checks for new mail, it runs a program called movemail that brings the mail in from the spool file. The MM variable movemail-path describes where movemail is on the system. Messages in your spool file are first copied into a file called .mm-newmail in your directory. From there, the messages are copied into your main mail file, the file set by the MM variable mail-file, which defaults to $HOME/mbox, i.e. a file named mbox in your home directory.
If you get any other mail file, or examine a mail file, MM will not run movemail when it checks, but will just display a message that there is new mail in the spool file.
The automatic get when MM starts up gives it write access to the main mail file, and lets it run movemail to bring in new mail. This action is controlled by the variable auto-startup-get, normally set to yes. If you set it to no, MM will start up with no current mail file, and you will have to give a get or examine command (which you might put in an .mmrc file).
MM checks for new mail automatically based on the settings of two variables, continuous-check and check-interval. At normal settings, the check is done under two circumstances:
The variable continuous-check controls whether to check in Read and Send modes (that is, at commands that result in a R> or S> prompt, and when the terminal is idle at the R> or S> prompts). Normally, it is set to no, so that you will not be interrupted while you are reading or writing messages. The command set continuous-check yes tells MM to check in all modes; remember to save-init if you want to save the setting.
The variable check-interval controls how often MM should check for mail when the terminal is idle. The value is the number of seconds; normally it is set to 300 (5 minutes). Remember that this refers to an idle terminal, a situation that may mean you have left your desk or are working on s