Valid email address rfc

According to the RFC (Request for Comments) 5322, a valid email address consists of a local part, an "@" symbol, and a domain. Here are the rules:

Local Part:

• The local part is the part before the "@"
• It can contain letters (a-z, A-Z), digits (0-9), and special characters (!, #, $, %, ^, &, *, +, -, _, ~)
• It cannot start or end with a dot (.)
• It cannot contain consecutive dots (..)
• It cannot exceed 64 characters in length

Domain:

• The domain is the part after the "@"
• It can contain letters (a-z, A-Z), digits (0-9), and special characters (-,.)
• It cannot start or end with a hyphen (-)
• It cannot contain consecutive hyphens (--)

Full Email Address:

• The full email address is the combination of the local part and the domain, separated by an "@"
• It can contain up to 254 characters in length

Here are some examples of valid email addresses:

• [email protected]
• [email protected]
• [email protected]
• [email protected]

And here are some examples of invalid email addresses:

• @example.com (missing local part)
• user..example.com (consecutive dots in local part)
• [email protected] (consecutive dots in domain)
• [email protected] (hyphen at the beginning of the domain)
• [email protected] (hyphen at the end of the domain)

Note that while these rules are specified in the RFC, some email providers may have additional restrictions or requirements for email addresses.