At an impasse

If she didn't write on the envelope then I would hazard a guess that the snail mail address you have is no longer valid for her and the forwarding order at the post office has expired. Usually if something gets returned for such a reason it comes back with one of those really attractive yellow stickers from the post office saying "Forwarding Order Expired" or something similar. You could try a registered letter but if you have an old address that would also be returned. Some email programs like Outlook have the option of attaching a confirmation receipt of sorts to the email that would indicate its delivery to the recipient email server or that it was viewed by the recipient so that might be helpful. Or if the snail mail addresses are in a county (like mine) that happens to list sale and ownership transactions as a matter of public record online, you could do a search on that street address. It wouldn't tell you if she is actually living there, but if you determine that the address is no longer in her name as of X date then it might be a confirmation that your Christmas card was returned due to a move. Food for thought anyway. Best, PADJ