OK, I’m a little confused by the situation here, so it might be worth getting some terminology clear. You’re talking about “front end” logins and a dashboard, and you’re also mentioning the env file.
You are correct in saying that “unlike other CMS platforms, users cannot log in universally from the front end”. Silverstripe has a powerful permissions system which grants different users varying levels of access, and how that works will depend on how the site was developed.
For now, my terminology is:
“Front end” - the actual website that normal visitors see
”CMS” - the admin pages of the site where you manage content, etc.
So, for now, I’m going to assume you’re trying to log into the actual CMS (eg. example.com/admin) rather than some kind of protected page of the front-end website.
There is no reason the credentials for CMS access would have changed when the site was migrated, other than someone removed them from the system. All those credentials are stored in the database, so they should have come along with the rest of the site.
Setting the SS_DEFAULT_ADMIN_* variables as described in this thread should allow you access to the CMS. You don’t have to use an email… just a username and password.
If that isn’t working, then it could be something to do with the new hosting environment. It may not be reading the env file, it may need to be refreshed, etc. and you may need to talk to a developer or your hosting provider for assistance.
If my assumptions are wrong, and you’re not trying to log into the CMS, but into another part of the site, let us know and we can try to help with that.
One last (important) note: If you use the default admin username and password in the env, please be sure to set up a proper user in the ‘Security’ section of the CMS and remove the defaults from the env as soon as possible - they should only ever be used for development environments / emergencies