While your sending volume is tiny, and while you're mailing an opt-in list, nonetheless it wouldn't hurt to order your emails in such a way so that they don't sorted mail by TLD... that is, don't mail all the @aol.com at once. Perhaps a random sort.

Again, this matters little for 500 emails, but I wanted to raise the issue that 'not mailing too fast' has implications for both the sender side and the recipient side.

(Of course, for really high-volume mailing, you establish relationships w/ AOL, MSN, etc and give them the heads up before bulk mailing into their system....)