Valid mail address

A valid email address is one that follows the standard format and syntax defined by the Internet Engineering Task Force (IETF) in RFC 5322. Here are the basic rules:

1. Local part: The local part is the part of the email address that comes before the @ symbol. It can contain:
   • Letters (a-z, A-Z)
   • Numbers (0-9)
   • Dots (.)
   • Hyphens (-)
   • Underscores (_)
   • The local part must not be empty.
2. Domain: The domain is the part of the email address that comes after the @ symbol. It must:
   • Contain at least one dot (.)
   • Not be empty
   • Not start with a dot (.)
3. Top-level domain (TLD): The TLD is the part of the domain that comes after the last dot (.) in the domain. It must be one of the following:
   • A valid TLD (e.g.,.com,.org,.net, etc.)
   • A country-code TLD (e.g.,.us,.uk,.au, etc.)
4. Special characters: The following special characters are allowed in an email address:
   • @
   • . (dot)
   • - (hyphen)
   • _ (underscore)
   • + (plus sign)
   • = (equals sign)
   • % (percent sign)

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 (no local part)
• example.com (no @ symbol)
• john.doe@ (no domain)
• john.doe@example (no TLD)
• [email protected] (multiple dots in the domain)

Remember that while these rules define a valid email address, they do not guarantee that the email address actually exists or is in use.