What Does \'3D\' Mean in HTML Email Code?

Understanding the Enigmatic Presence of "3D" in HTML Code

When examining the source code of a received email, you may encounter peculiar HTML elements like the ones you've encountered:

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This seemingly cryptic "3D" isn't actually related to three-dimensional rendering in the usual sense. Instead, it's an integral part of an encoding scheme known as "quoted-printable."

Quoted-printable encoding is used to ensure that non-ASCII characters, such as foreign language characters or symbols, can be accurately transmitted and displayed in emails. It works by representing each non-standard email octet (an 8-bit unit of data) as an equal sign (=) followed by two hexadecimal digits that correspond to the octet's value.

However, email transportation systems may sometimes interpret a standalone equal sign (=) as an indicator of quoted-printable encoding, requiring it to be encoded as well. To represent the "=" character in such scenarios, quoted-printable uses the hexadecimal value 3D, which is the ASCII code for "=". Therefore, the seemingly enigmatic "3D" you've observed is simply the result of the encoding process, ensuring that the equal sign is correctly interpreted and displayed in the recipient's email client.

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