Just a nit, but consistency would probably help and avoid potential issues:

• In composition, when you autocomplete to a list which has a space in its name (My list), it will come out like this:
  My list <My list>.
• However, when you drag the same list from Contacts Sidebar or address book window into composition's addressing area, it will come out with added quotes like this:
  My list <"My list">

Fortunately, both variants work correctly, but it's confusing (and potentially error-prone) to have different syntax for the same thing.

Expected:

• no quotes added when dragging mailing list into composition's recipient area.
• continue to add quotes only for contacts with regular email addresses as needed (due to spaces etc.).
• Or perhaps Aleca wants to seize the opportunity and render a mailing list item in a recipient field in a nicer visual way, perhaps with a mailing list icon, in the following mockup represented as (pp):
  (pp) My list