I used to have a large excel sheet, where I keep all the email addresses and phone numbers, as well as their countries etc.
When Airbnb started to mask the emails, this did not have any more sense because those email addresses get invaild after 30 days of check-out.
Most of the times, I like to keep in touch with my guests, no matter they visit again or not.
Since couple of weeks, I’m using an App called Your Porter App (yourporter.com), which keeps the all guests data on my smartphone. It even adds my guests’ phone numbers with their name to the contacts of my phone! It is very useful if you have several listings and you get a text on your mobile phone from unknown number saying “Hey Maria, we are coming to your apartment soon or Hey Maria, the heater does not seem to be working” At lease I can answer an incoming call with their name
The best part of it, that i can send my guests an arrival form to collect their arrival details, flight numbers and real email addresses for my records. Those masked airbnb emails do not work sometimes and they expire after a while.
If you take your Airbnb business seriously and manage it like a real guest relations professional, Your Porter may create a good difference for you. It did for me so far.