I had an incident when my barber decided to use online appointment booking using Calendy.
For reasons, I often search for some of my emails and aliases.
To my delight, my first name and an email address was publicly visible along with the conversation.
Calendy made some corrections to their service soon after.
Trust no service to be secure.
Use a disposable/junk email address that doesn't connect to anything secure or you need kept private like bank accounts etc
Why you are being downvoted is amazing. This is a legitimate question of privacy. And it's one that too many blindly trust in a service just because it says it can be trusted.