Encoded words allow non-US-ASCII characters to be encoded as US-ASCII and thus placed into email headers.
Encoded words are often used in the Subject header, especially when the Subject is in another language, such as Spanish:
Question: Is there a legitimate reason to use an encoded word in any header other than the Subject?
Examples from RFC 2047
- Display Names in email addresses: To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?=
- Comments: From: Nathaniel Borenstein (=?iso-8859-8?b?7eXs+SDv4SDp7Oj08A==?=)
I actually received one of these recently. The "guilty" party was Airmail. Here's the headers (with the email address changed):
To: "=?utf-8?Q?john=40doe.org?=" <email@example.com> Message-ID: <etPan.534b7be1.6c8b4667.233@myMac.local> Subject: check this out X-Mailer: Airmail (237)