Why Use Berkeley sendmail?

Security fixes

Because of its function and complexity, sendmail has a large number of security holes. When a new hole is discovered, it's patched almost immediately in Berkeley sendmail, and a new version is released. Most vendors (whose sendmails are usually based on old, buggy, insecure versions of Berkeley sendmail) will often refuse to release patches, and when they do it is not usually in a timely fashion.

Features

Berkeley sendmail is under constant development by Eric Allman and a team of free software writers throughout the world. New features, such as spam protection, are integrated into Berkeley sendmail before any of the vendor sendmails.

Standards

Berkeley sendmail is the de facto standard for the academic Unix community, and even for some of the forward-thinking industrial community. There's a wealth of information available for it all over the Internet.

Support

Although a vendor may provide support for their sendmail implementation, it is often costly and they may not be as responsive to your problems as you'd like. Berkeley sendmail is used at a tremendous number of sites around the world, and if you have a little initiative to work on your own problem, there are almost always other knowledgeable sendmail administrators willing to help out.