RFC 5321 specifies that the body of an email be encoded as 7 bit, US-ASCII. The 8BITMIME extension allow the body to be encoded as 8 bit. An SMTP server can advertise that it supports 8BITMIME in its response to the EHLO command:

250-smtp.example.com at your service

And the SMTP client can tell the server that it will use this extension in the MAIL command:

MAIL FROM: <john@example.com> BODY=8BITMIME

Most SMTP servers today support 8BITMIME and do so with UTF-8.

Question: Are there any SMTP servers or email clients that support 8BITMIME but do so by using an encoding other than UTF-8? If so, which ones and what encoding?


The mail server itself does not need to support any encoding. It only advertises that it can handle mail bodies with 8 bit (instead of 7 bit). Old servers not supporting 8 bit could delete the first bit of the data. Therefore it does not matter which encoding you are using if the server supports 8 bit. Only the destination email client must support your encoding (e.g. UTF-8 or ISO-8859-15).

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