Valid emails (with a plus sign “+”) are not allowed

This issue was already raised here https://wordpress.org/support/topic/email-with-plus-sign-is-invalid/ , however it has not been resolved.

Perfectly valid email addresses that contain a plus symbol (e.g. <myself>+<anything>@gmail.com) can sign up but then get an error message when clicking on the email confirmation link.

This is a common practice, especially when signing up for newsletters, so it would be great if this could be fixed.