Header and envelope encoding
SMTP standards require envelope commands and header information to be sent in the US-ASCII character set.
No sending SMTP system is
permitted to send envelope commands in any character set other than
US-ASCII; receiving systems SHOULD reject such commands, normally using
"500 syntax error - invalid character" replies.
2.2. Header Fields
Header fields are lines composed
of a field name, followed by a colon (":"), followed by a field body,
and terminated by CRLF. A field name MUST be composed of printable
US-ASCII characters (i.e., characters that have values between 33 and
126, inclusive), except colon. A field body may be composed of any
US-ASCII characters, except for CR and LF. However, a field body may
contain CRLF when used in
header "folding" and "unfolding" as described in section 2.2.3. All
field bodies MUST conform to the syntax described in sections 3 and 4
of this standard.
The MIME Content-Type header is used in message bodies to specify alternate character sets.
Bad header example
$ cat -v bad.header | grep '^From:'
In cat -v output. M- represents a character outside the ASCII range (metacharacter).
$ grep '^From:' bad.header | od -c
F r o m
: < f
r a n 347 o i s .
0000020 j a u
c o t @ e
x a m p l
e . c
0000040 o m > \n
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Last modified: 2006/03/09