Question

I just need to know what the name for the mail in:

*mail.*google.com

would be named

I thought ‘custom domain prefix’ made sense, but that doesn’t seem to be it.
Please provide a link to documentation if possible, or just a proper search query.

Also, would it be a good idea to use these prefixes? Basically I have a site called smokelessmi.org and I want to make a prefix a2.smokelessmi.org for the city (Ann Arbor, Michigan) since this is a localized website.

Eventually I want to add other cities in Michigan, but I’m just starting with this one.

Answer 1

Not surprisingly there’s a plethora of rfc’s (rfc1591 rfc2606 and rfc2181 to name just a few) that talk about the structure of domain names, and this quote from rfc2181 stresses the hierarchical nature of DNS

Occasionally it is assumed that the Domain Name System serves only the
purpose of mapping Internet host names to data, and mapping Internet
addresses to host names. This is not correct, the DNS is a general
(if somewhat limited) hierarchical database, and can store almost any
kind of data, for almost any purpose.

So, to the left of your Top Level Domain (.com in your example) and what’s quite often called second level domain (also used in the aforementioned rfc2606 and also in rfc920) or in short domain, you can still have a whole hierarchy of names. Personally I like to think of the leftmost one as the host name, because if you’re addressing a service chances are that the most specific one represents a computer. The "intermediate ones" are commonly called subdomains.