As the internet has expanded to a thousand new domain extensions (known in the industry as new generic top level domains, or new gTLDs), not all websites have yet been updated or upgraded to support these new domain extensions for user email addresses, sometimes used for username login access and for vital on-going communications.
You can get a sense of how popular websites are handling user emails that have new gTLDs from this universal acceptance testing conducted by the .CLUB top-level registry. (in summary, 65% passed, and that means 35% are not yet fully-supporting new gTLD emails.)
[UA-Discuss] Acceptance Tests done for sites
Dirk Bhagat dirk at get.club
Wed May 18 13:15:55 UTC 2016
As part of .Club's effort prior to UASG, .club had hand tested around 600 popular sites [mostly from Alexa] for their ability to accept *.club* email addresses.
Here is the testing spreadsheet we used: https://docs.google.com/spreadsheets/d/1WIhKvD7mvK7xHyRWGNK1AcDTK7Yhdt69RXuPKcpTIZA/edit?usp=sharing
This spreadsheet breaks the list down into a few categories:
Although there is a lot more work to be done, I believe it's a good starting point.
-- Dirk Bhagat
.CLUB DOMAINS LLC.
100 SE 3rd Ave, Suite 1310
Fort Lauderdale, Fl, 33394