The dot at the end has a technical meaning in two different contexts. The first is to disable search lists in the DNS stub resolver. If you try to look up, say

The dot at the end has a technical meaning in two different contexts. The first is to disable search lists in the DNS stub resolver. If you try to look up, say 'ai', then the sub resolver is likely to append your current domain name during the lookup. Looking up 'ai.' disables that. The other use is in DNS zone files where everything that does not end in a '.' get the name of the zone appended. The for mail (SMTP) the dot at the end is implicitly present, and adding one is not allowed. HTML/HTTP basically doesn't define semantics with respect to the dot at the end. That's why "www.example.org" and "www.example.org." are different. They are different strings, and nobody defined them to be equivalent. At the same time, the name is just passed to the stub resolver in many cases. So search lists may be applied under the hood.