A “SRV” or Service Locator record is a general record that can be used in a generic fashion rather than creating protocol-specific records such as MX.
DNS
What is a NS record?
A “NS” record or Name Server record identifies an authoritative DNS server for a specific zone.
What is an MX record?
“MX” (Mail Exchange) records are used to specify what server on the Internet is running e-mail software that is configured to handle e-mail for your domain. If you want your ISP to handle routing the e-mail for your domain to you, you need to specify the domain name or IP address of your ISP’s mail server.
In addition, you can specify the rank of each mail server when you have more than one. Make sure your ISP knows that you’re using their servers to route your domain’s email, or all your e-mail will “return to sender”!
What is a CNAME record?
“CNAME” records, short for “Canonical Name”, create an alias from a domain name to another. You could create an alias from “yahoo.mydomain.com” to “www.yahoo.com”, and every reference to “yahoo.mydomain.com” would go to the other location, regardless how yahoo changed their IP addresses!
Be careful, however; CNAMEs won’t work everywhere. If you create an MX record, and the name used for the mail server was defined using a CNAME, you might lose e-mail.
What is an AAAA Record?
Whereas an “A” record is used for IPv4 addresses, an “AAAA” record ties a domain name to an IPv6 address in the same manner.