ksh MAILCHECK Environment Variable

The MAILCHECK environment variable contains the minimum number of seconds that must elapse before dbx checks for incoming mail. The check is performed just before printing the prompt, if $MAILCHECK seconds have elapsed since the last check. If $MAILCHECK is null or is zero, the check is performed before each prompt. If $MAILCHECK is unset, or is set to a non-numeric value, checking for mail is disabled. The default is 600 seconds (ten minutes).