Normally, makemap refuses to allow keys without data. That is, the following infile:

bob     Good User
ted
alice   Gone User

would produce the following error when read by makemap:

makemap: hash: line 2: no RHS for LHS ted

But, sometimes it is necessary to initialize or fill databases with new information when the data is not known but where that lack of information is not harmful, or where the data is not required. In support of such needs, makemap allows this -e switch. With it, keys that lack a data portion are allowed to populate the database.

Sometimes it is desirable to populate a database with keys only. For such databases, the key's presence is the only information of interest. Consider the following K configuration command:

Klocaluser hash -m /etc/mail/localusers

Here, the -m database switch (-m) tells sendmail to look up the key, but not to fetch any data.