1. Do nothing - there would probably only be a small part of the list visiting during the down-time. When they receive the next regular email, they will know all is OK anyway.
2. Send an email to the list apologising for the inconvenience of the downtime and leave it at that - anyone that was inconvenienced has received an appropriate apology and will know it's ok - the rest of the list is alerted to the server issue.
3. Send an email to the list apologising for the inconvenience of the downtime and offering a free bonus.
I'm tending towards one of these options. However, I don't want to influence any ideas or vote, and I'd be very grateful for your thoughts on which of the above you think is the best course, or whether you think that there is another better course of action to take. Thanks in advance for your ideas.