spop - POP mailer
The spop command delivers mail to the Post Office Protocol (POP) spool area on your local system. POP is a service that allows you to set up mail so that it is delivered on a larger system, rather than on a smaller system.
Normally, you do not issue this command. Instead, the mail delivery
system uses this command as part of its normal processing.
Commands: popaka(8), popd(8), popwrd(8)