[freeAgent]

Unless mydomain[.]com is used by more people than just you and maybe your family, doesn’t the domain itself serve as a unique(ish) identifier? I think public aliasing services offer better anonymity, but they’re also blocked by some services.

[blep_]

For humans who are paying attention, sure. In practice, not really, because it's all done by scripts without an easy way to query "is this domain shared".