I'm not sure to understand the question. If a user has already used the "Sign in with SimpleLogin" on CollAnon, they will be automatically logged in the next time. There's a demo on https://forum.simplelogin.io
Even Gmail spam filtering is one of the best, it has its limit. The solution is to use different email addresses (aliases) to control who can send us emails: if we start to receive spams at one address, we can just disable it.
I think supporting only social login in the MVP totally makes sense [1] as account verification/authentication requires boilerplate code that isn't core to your product.
Even though I'm the developer of a "rival" service [1], it's a good news that more and more email aliases services are created. That means email alias is becoming mainstream.
I created a similar service called SimpleLogin. [1] and hope to have a similar success some day! Using email aliases is an efficient way to protect our privacy and hopefully the concept becomes more mainstream in the future. I'd suggest removing the "disposable" mention as otherwise email aliases would be put in the same category as temporary email services, which increases the risk of having your domain blocked.
We believe having a different identity for each website/service is an effective way to protect our privacy and that's why SimpleLogin is created.
All components in SimpleLogin is open-source, including the server, website, browser extensions, and mobile apps. SimpleLogin can be self-hosted and supports security-oriented features like PGP, WebAuthn.
The server is a Python/Flask application backed by PostgreSQL as database and Postfix as email MTA. The web front-end is coded with VueJS and Bootstrap for styling. Mobile apps are coded in native.