@Caroline28, after payment is made, you can ask your guest for his private mail. I do this for full apartment rentals, where I need to send a contract. Pictures pass after booking but pdf files are blocked by the spamfilter half the time (it's always the same contract, but half the time it does not pass, go figure).
So I explain nicely that I need it for the contract and give them mine. It's not censored after booking. However, if you wish to get phone numbers or mail addresses a bit after the stay, it's again hidden.
(You may not need a contract, it's a legal requirement in my country. But you can still ask. They can refuse.)