1. Regression from 3.x, using admin+foo@localhost.test for install on both versions and it works on 3.x
2. For mine, it is failing in the EmailRule after the address is converted to punycode

Concerning punycode mails.
I can't reproduce the issue when doing a clean install of 4.0-dev branch.

It also works fine in Users Manager
When creating new user through Users Manager an email of the type admin@джумла-тест.рф is or admin+foo@localhost.test is accepted OK
No success message though.

can you folks test with latest branch?

Works as expected:

System information

4.0.0-dev
Multilanguage Site (4 Lang.) & Sample Data
macOS Sierra, 10.12.6
Firefox 57 (64-bit)

MAMP 4.2

• PHP 7.0.22
• MySQLi 5.6.35

What @anibalsanchez experienced (i was next to him when that happened) was a failure in the client side, so something either on the punycode or the validation needs some love

I can't either reproduce when Creating an account or editing a profile in frontend

I've just tested on the latest J4 A2, and the issue remains.

• NOTE: The error is reported at the top of the page, after you click on "Install Joomla"
• So, it looks like the email is accepted, but it is validated and rejected in the final step

Checking the validator, the value of the field has a space instead of +, so something else is going before the validation.

I can no longer replicate this in the installer. I can only assume it was resolved elsewhere so I shall close it. If I am mistaken it can always be reopened