How affect for each user a subdomain ? with module domain-acces, we can  manage domains and subdomains,
example: 


domain.com is my first domain.
user1.domain.com is affected to user1
user2.domain.com is affected to user2


but user1 can connect to user2.domain.com that is my problem.
Unfortunately, it looks like this isn't what Domain Access was intended to do, as its focus is "sharing information across subdomains" rather than restricting it:

https://www.drupal.org/project/domain/issues/480716

In the comments there is a link to a code library that can achieve what you want, however.