[dgacmu]

I'm probably out of date, but Google's advanced protection at one point did account recovery via postcard to your home address. High latency but pretty good as a fallback.

[HWR_14]

Postcards are the least secure form of mail. I would hope it uses a security envelope at least.

[itintheory]

There are many good options. [1]

[1] https://news.ycombinator.com/item?id=48321089