The Proton instant alias system e.g. username+othersite@proton.me is rejected by a majority of sites. It makes the service close to useless. Other services use a hyphen instead and it is accepted everywhere. Proton must change this. It's not a big change. Make the + and - interchangeable. Users with established + aliases can continue using them but others that use the - sign instead should be able to.

This isn't a big ask but the system now is dysfunctional and ineffective.