How should the X-Brightmail-Trakcer header be folded.
According to RFC5322 "Internet Message Format", it is recommended that an MTA split a long header line into multiple lines.
2.1.1. Line Length Limits
There are two limits that this specification places on the number of
characters in a line. Each line of characters MUST be no more than
998 characters, and SHOULD be no more than 78 characters, excluding
2.2.3. Long Header Fields
each header field is logically a single line of characters comprising
the field name, the colon, and the field body. For convenience
however, and to deal with the 998/78 character limitations per line,
the field body portion of a header field can be split into a
multiple-line representation; this is called "folding". The general
rule is that wherever this specification allows for folding white
space (not simply WSP characters), a CRLF may be inserted before any
Symantec recommends that an MTA which integrates with SMG-SP fold the X-Brightmail-Tracker header,
so that the number of characters on each line does not exceed 78 characters.