How do I configure my server to recognize both .htm and .html?
Many web servers run Unix or another operating system that
allows long filenames. Many users, on the other hand, are
stuck with 8.3 filenames under MSDOS and Windows 3.1.
As a result, many users give their documents a .htm
extension and are surprised when servers fail to
automatically recognize this.
Under the NCSA and Apache web servers for Unix, this can
be easily corrected by adding the following line
to the srm.conf file:
AddType text/html .htm
Most servers now ship with both .html and .htm recognized by default.
World Wide Web FAQ