If you intend to write an RFC822 parser, please, please take
the advice of everyone who has done so until now:
 
Do not write a parser which accepts only what is specified in
RFC822 exactly and nothing else. Rather, write a parser which
accepts and tries to understand everything which remotely looks
like RFC822! Otherwise you will get into endless trouble.
 
Example of illegal RFC822 things you should accept:
 
John Smith <JS@HOST>
should correctly be
"John Smith" <JS@HOST>
 
Message-ID: <AAA&BBB@CCC>
should correctly be
Message-ID: <"AAA6BBB"@CCC>
 
Message-ID: <AAA@BBB> (From my perfect mailer)
should correctly be
Message-ID: <AAA@BBB>
 
etc. etc.
 
And please do accept things, even if they are on different lines.
Thus you should accept:
To:     "a very very very very very very very very very long name"
        <AAA@BBB>
Even though the name is split on several lines.
 
I could give you unlimited more examples.