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

Mysterious "3D" in HTML Email

In the HTML code of a received email, you may encounter lines similar to these:

<td>

These "3D" sequences may seem confusing. They are not used in standard HTML formatting.

Decoding the "3D": Quoted-Printable Encoding

"3D" in this context is not a three-dimensional element. It is part of the quoted-printable encoding system, which is used to represent non-ASCII characters in emails.

In quoted-printable encoding, non-ASCII characters are converted into an ASCII representation consisting of an equal sign (=) followed by two hexadecimal numbers representing the octet value of the character. For example, "é" (octal value 233) would be encoded as "=E9".

The "3D" sequence specifically represents the equal sign (=) itself, which is encoded as "3D" (octal value 61). This is because the equal sign is used as the delimiter for quoted-printable encoded characters, and it must therefore be encoded itself.

Therefore, the HTML code you provided contains elements with styles applied to them, and then the octet value of an equal sign (=) is represented as "3D" within the style attribute. This is part of the quoted-printable encoding process, which ensures that non-ASCII characters can be correctly transported and displayed in emails.

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