Our focus is on holiday greetings. This is true. There are people with limited hard drive space. There are people who can receive a limited number of messages per day. There are people who pay per minute charges to get their email at home.
Many lists archive their messages.
Archiving 500-1000 messages of Christmas cheer eats valuable space. Posting an offer to do lookups in a resource that you have access to. Briefly post to the list how you researched your ancestors in the area or region that is the list's focus. After all, that's what the season is supposed to be about. Place a brief holiday greeting at the end of your post or message.