Entity 303 email header

A blast from the past!

Entity 303 is a type of email header that was commonly used in the early days of email, particularly in the 1990s and early 2000s. It's a way to encode special characters in email headers, such as non-ASCII characters, using a specific syntax.

Here's an example of an Entity 303 encoded email header:

Subject: =?UTF-8?B?Q2FycmF5IEkgZm9yIGJ1c2luZXNz?=

In this example, the Subject header contains a encoded string using the UTF-8 character set, Base64 encoding, and the ? syntax. The ? is used to indicate the character set and encoding used.

The decoded version of this header would be:

Subject: Special characters in email headers

Entity 303 encoding was used to overcome the limitations of early email systems, which often couldn't handle non-ASCII characters in email headers. It was particularly useful for sending emails with non-English characters, such as accents, umlauts, and other special characters.

However, with the advancement of email standards and the widespread adoption of Unicode, Entity 303 encoding is no longer commonly used. Modern email systems can handle non-ASCII characters in email headers without the need for encoding.