Mass Email Christmas Greetings without spamming

I think the answers to these questions depend on several factors:
1) Are you hosting your own SMTP server?
2) If not, does your ISP have any maximum sending limits?
3) Are you sending Emails to people who already do business with your company?
4) Do you provide them with a way to opt out?

The BEST solution is to add a mailing list feature to your web site.  This will allow users to sign up on their own, and if you use a double-opt-in solution (you have to also follow the link to make your registration permanent), then you should not run afoul of any spam regulations.  Again, the SMTP gateway host is likely to be a big part of the answer, so contact your ISP or hostiong company, if needed.  Of course, users can always flag a message as spam just because they don't like your message, and if enough do it, then you may still get flagged as a spammer.  I doubt most people do this with holiday greetings, but I could be wrong.  

With ONLY the info already posted, I would simply make up a small email message, then automate with a tool like KeyText.  This keyboard macro tool can be used to extract Email addresses from an Excel spreadsheet, then build an Outlook Email directly to each recipient.  As it works only as fast as your local machine/keyboard, it won't be able to send too many messages per second to run into the spam issue, but it may take it all night to run, too.