What are all the valid ways to represent an IP6 address w/ an email

Given user@1:2:3:4:5:6:7:8 how many different ways can this be represented in an unnormalized way.

I found in a test suite for emails Dominic Sayers email test suite the following email. The host was the part that interested me particularly the wrapped of the number notations with "IPv6["

"first.last@[IPv6:::12.34.56.78]";

Are the brackets开发者_运维问答 only allowable for emails or ip6 addresses as well ?

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IPv6 literal addresses should be expressed in brackets for URLs, e.g. http://[::1]

http://www.ietf.org/rfc/rfc2732.txt

This follows through for email addresses, e.g. root@[127.0.0.1] or root@[IPv6:::1].

It's to avoid the case of say dead:beef:1 attempted to be resolved as the DNS host dead.