Handy maximum email message body values to know when debugging email line-folding problems.
Generally if ! or !+ characters are inserted into long email lines, the solution is use shorter lines (insert newlines) or use quoted-printable encoding.
|RFC821||1000 including CRLF|
|sendmail standard ESMTP||990|
RFC 821: “The maximum total length of a text line including the <CRLF> is 1000 characters (but not counting the leading dot duplicated for transparency).”