[sarciszewski]

I'd recommend going base32 instead of base64 (case sensitivity won't screw anything up) and not padding with = characters. I know not padding violates RFC 4648 but I don't know anyone who's used to a = in their email address.

[StavrosK]

Base32 would be too long, but maybe the equals sign could be elided, yeah.

[rakoo]

Base58 it is, then (no non-alphanumeric characters so you can double click and it will select the whole string, no similarly-looking characters you could mistype (1 and l, 0 and O...))

(https://en.wikipedia.org/wiki/Base58)