Ordinarily, sendmail
will normalize a key to lowercase before looking it up in a database.
If the keys in the database are case-sensitive
("TEX" is considered different from
"tex," for example), the
-f database switch should be used to prevent this
normalization. Note that if the -f switch is
omitted (the default), the database must have been created with all
lowercase keys (also the default).
Also note that when the -f switch is used with the
regex database-map type, it causes the regular
expression match to be made in a case-insensitive manner.
