determines the behaviour in the event
iconv_mime_decode() encounters a malformed
MIME header field. You can specify any combination
of the following bitmasks.
Bitmasks acceptable to iconv_mime_decode()
If set, the given header is decoded in full conformance with the
standards defined in » RFC2047.
This option is disabled by default because there are a lot of
broken mail user agents that don't follow the specification and don't
produce correct MIME headers.