OK I'm beginning to agree here as well. Generally speaking the answer is no, they do not.
Some domains correspond to the namespace of a local system authorization file and nothing else.
Some correspond to entries in some database. Some map onto other namespaces, like FAX numbers or printer names or whatever. Now, you could build a private thingie that put local part information in the DNS if you wanted to. It would not be a standard use of the DNS and I would question the choice on technical grounds, but you could do it. Depends on the system.