Unfortunately even the "quotes", while typical, are optional; I have lots of examples of both ham and spam without the quotes. The rule is that everything from the ':' up to the '<' is the description (and nearly anything is "legal"). To show examples, here is an example from RFC2821 appendix D.3
IIRC, the only time quotes are required is when there are funky characters, such as some punctuation (as in my last name), in the description/name. The majority of MUAs just put the quotes in to avoid having to decide if they are required.
Daryl
