How many sub-domain are allowed for an Email Id?

问题:

How many subdomains are possible for an Email address? For Example: [e-mail] like that....

回答1:

There isn't any constraints based on subdomain count.

There is limitation of lengths parts of e-mail address in RFC821

user

The maximum total length of a user name is 64 characters.

domain

The maximum total length of a domain name or number is 64 characters.

path

The maximum total length of a reverse-path or forward-path is 256 characters (including the punctuation and element separators).

limitations in RFC2821

local-part The maximum total length of a user name or other local-part is 64 characters.

domain The maximum total length of a domain name or number is 255 characters.

and newest in RFC5321

4.5.3.1.1. Local-part

The maximum total length of a user name or other local-part is 64
octets.

4.5.3.1.2. Domain

The maximum total length of a domain name or number is 255 octets.

4.5.3.1.3. Path

The maximum total length of a reverse-path or forward-path is 256
octets (including the punctuation and element separators).