maildir-utils binary package in Ubuntu Xenial s390x

 mu is a set of utilities to deal with Maildirs, specifically,
 indexing and searching.
  - mu index - recursively scans a collection of email messages, and
    stores information found in a database.
  - mu find - searches for messages based on some search criteria.
  - mu mkmdir - creates a new Maildir.
 .
 mu uses libgmime2 to parse the message, and Xapian to store the message data.

Source package