If your service tells me that myname+servicexyz@gmail.com is an invalid address, you have to live without me. I can't count how many mails I sent to websites incorrectly validating email fields. However, password validation is mostly even worse. Just stop over-validating already!
Agreed that password validation is the worst. (Github, I'm looking at you.)
Even worse than excessive validation is when they make you change your password often, for no apparent reason.
On some sites that do both (ahem Apple), the only way I can login if I haven't been there in awhile is the security questions or the password reset mechanism.
Wow, I never noticed that Github enforces password rules, as well (Must contain one lowercase letter, one number, and be at least 7 characters long.). My passwords are usually HMAC-based, so they'll most likely validate.
even validation of first & last names is usually awful. For instance many sites tell you that having a dash "-" in your first name is invalid... yet a lot of French (first or last) names contain that character..
Those who happen to own domain name and some small hosting plan with Cpanel can easily redirect all mail to that domain for specific email address. This way you can replace plus sign with dot that works everywhere.
