Some of this behavior is just how email is defined to work in the original specs. For example, it was agreed upon 15-20 years ago that you can freely add a plus sign and any other text to your address. So if you have
account@gmail.com, account+smith@gmail.com will send mail to you. Or account+walmart, account+bankname, etc so some people are recommending the plus sign to track what emails are for what.
I don't remember the definition for how dots are supposed to work.
Many people have corporate addresses of their first name dot their last name @ work.com. That's because when you work at a corporation, they don't want you to have a handle-ish name like "undertoad". It's considered unprofessional.
I write the above paragraph because we will laugh so heartily at it in 20 years.