Some website’s registration edits don’t support the gmail plus sign option.
We have to insist that they do or not use their sites.
To refresh your memory, GMAIL (to their credit) has innovated by adding the capability to allow a plus sign in the email address. So if your gmail email address is abcdef @ gmail dot com, then you can put anything you want after a plus sign. So if email comes addressed as abcdef + fedcba @ gmail dot com will get delivered to your email account and you can test on that stuff after the plus sign.
It’s a great spam preventive.
For example, I give each use of my gmail address a unique unguessable random code. (You expected different from a fellow who uses long strange email addresses?) Any email that arrives without a “plus code” is suspected of being spam. Should I get spam, I can pinpoint where the breakdown occurred.
So, if a website
would will NOT accept a plus code, I don’t use it.
(Note correcting an instance where the fingers led a life of their own.)