RFC 2822 seems to state the "Subject:" and other keywords are case-INsensitive

... and to make things worse, "2.2.3. Long Header Fields" allows to wrap lines so that the content is split over several lines. This is a single logical header line, split over several physical lines:

Subject: Mail
 parsing looks
 simple until you
 have 
 read 
 the 
 RFCs
[download]

Additionally, RFC2047 allows encoding of non-ASCII characters.

Any mail parser should be able to handle that, too.

Alexander