We are not offering a spam filter per se, but a spam management relying on your provider spam filter: Your provider has special software that detects suspicious emails and puts them in spam. That will be reflected in BlueMail as well as the web client of the provider.
Any settings done in BlueMail complements your provider’s actions, and we cannot undo or override your provider. So essentially:
If you mark emails as spam in BlueMail, you can then unmark them to trust them again. This can be done both for a single email address and for a domain.
However, if your provider filter identified something as spam, it will move the emails to Spam and we will not be able to change this. Even if we tried, your provider would move it back to spam…
To actually mark as trusted if it was marked as spam in BlueMail: Go to the Spam folder | Open an email | Tap the 3-dot-menu | Unmark as Spam | confirm with OK.