7bit
MIME transfer encoding labels meaning the content is not encoded: 7bit is ASCII only in short lines, while 8bit may also contain bytes above 127.
What it means
RFC 2045 calls 7bit, 8bit and binary identity encodings: the header only describes the data, which was not transformed. 7bit, the default, means US-ASCII in lines of at most 998 octets. 8bit also allows bytes above 127, such as raw UTF-8, in lines of that length, and may only be sent to a server that announces 8BITMIME. Binary drops the line rules as well and needs the BINARYMIME extension.
When an 8bit part meets a server without 8BITMIME, the sending server has to convert it to quoted-printable or base64 or fail the delivery, and the conversion breaks any DKIM signature. RFC 6376 therefore advises signers to encode 8-bit content before signing.
Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
All 432 terms in the glossaryThe wiki: blocklists and bounce codes