I heard the advice to send written thank-you notes even when everyone is working from home and we don't have people's home addresses (and even if we did using them would be creepy). The advice was to send it to the company's business address and it would probably be forwarded by the company to the person's home address. It seems like imposing additional work on the poor admin who has to risk their health to go to the office and get the mail.
Also, when we are interviewing over Zoom and people are at home, we won't have their phone numbers either, so that part of follow-up doesn't work either.
Just e-mail for now? Thoughts?