**1. Email Address Basics:**
– Message Transport using SMTP protocol
– DNS lookup for recipient’s domain
– Email aliases and catch-all addresses
– Syntax and format of an email address
– Maximum lengths for local-part and domain
– Evolution of email address notations
– Display Name for recipients
– Local-part and its significance for mail relay systems
– Email Address Security against spoofing and phishing
**2. Local-Part Details:**
– Unquoted and quoted local-part
– Allowed characters in unquoted local-part
– Restrictions on special characters
– International characters in UTF-8
– Case sensitivity of local-part
– Sub-addressing with tagging using plus and minus signs
– Example of tagged address
– Alias to a prefix of the local-part
– Delivery address variations
**3. Domain Guidelines:**
– Domain name requirements
– Label limitations and LDH rule
– Use of IP address literals in square brackets
– Internationalized domain names with non-ASCII characters
– Examples of valid and invalid email addresses
**4. Validation and Verification:**
– Use of email addresses for user validation
– RFC specifications for email address structure
– Validation techniques and sender reputation
– Correct email address not guaranteeing mailbox existence
– Various validation techniques available
**5. Internationalization of Email Addresses:**
– IETF efforts for internationalization
– UTF-8 encoding for non-ASCII characters
– EAI Working Group and RFCs for non-ASCII email transmission
– EAI concepts and benefits
– International Email Adoption in various countries
– Examples of internationalized email addresses
An email address identifies an email box to which messages are delivered. While early messaging systems used a variety of formats for addressing, today, email addresses follow a set of specific rules originally standardized by the Internet Engineering Task Force (IETF) in the 1980s, and updated by RFC 5322 and 6854. The term email address in this article refers to just the addr-spec in Section 3.4 of RFC 5322. The RFC defines address more broadly as either a mailbox or group. A mailbox value can be either a name-addr, which contains a display-name and addr-spec, or the more common addr-spec alone.
An email address, such as john.smith@example.com, is made up from a local-part, the symbol @, and a domain, which may be a domain name or an IP address enclosed in brackets. Although the standard requires the local-part to be case-sensitive, it also urges that receiving hosts deliver messages in a case-independent manner, e.g., that the mail system in the domain example.com treat John.Smith as equivalent to john.smith; some mail systems even treat them as equivalent to johnsmith. Mail systems often limit the users' choice of name to a subset of the technically permitted characters.
With the introduction of internationalized domain names, efforts are progressing to permit non-ASCII characters in email addresses.
