For example, I just signed up for a second line of internet for my homelab with Spectrum. I provided my email address "[email protected]". The sales rep's systems accepted it just fine, but when I try to create an account on their online portal, it's suddenly not a valid email address.

This is arguably worse than requiring passwords to contain symbols and numbers.

I bet there's more weird rules that are hurting other people as well.

RFC 2822 Section 3.2.4 [1] says:

    atext           =       ALPHA / DIGIT / ; Any character except controls,
                            "!" / "#" /     ;  SP, and specials.
                            "$" / "%" /     ;  Used for atoms
                            "&" / "'" /
                            "*" / "+" /
                            "-" / "/" /
                            "=" / "?" /
                            "^" / "_" /
                            "`" / "{" /
                            "|" / "}" /
                            "~"

I suspect what's happening is they've got some rule against the word "spectrum" or something. Or perhaps they're a bad company and just HAVE to have base-level addresses to sell to the advertisers?

- [1]: https://www.rfc-editor.org/rfc/rfc2822#section-3.4.1