SlackBuildsOrg/system/mailutils

GNU mailutils is a powerful protocol-independent mail framework. It
provides a set of libraries for writing flexible mail-handling
software, as well as a number of utilities for both local and remote
mail handling. Among the utilities provided are pop3 and imap4
servers, sieve mail filtering utility, mailx-compatible mail client
and others.

NOTE: This package overwrite some files in Slackware's core packages:
- elm
- mailx

If you removed mailutils, don't forget to reinstall them again.