How can you specify a group list as a recipient of a message?
Longer answer: SMTP requires the individual names within the group list to be specified in separate RCPT commands. Sun's SMTP provider sends them as a single command and the server rejects them. You can create an InternetAddress for the group list, the sending though will fail.
Group lists are a specific type of valid email address in the RFC822 spec under section A.1.5. The 'To:' header of an email sent to a group list would look like:
To: Announcements: firstname.lastname@example.org, email@example.com;
To: Comment: address, address;
They allow you to provide a comment on the list of people who are receiving the email. The comment above is "Announcements". The interesting thing is that the addresses portion may be blank leaving you with just the comment portion:
Using a group list with a blank address section is a standard list server technique.