Note: i am not looking for RFC rule or IETF rule also.
I m looking for rules that are used while choosing an user name for following email providersAOL Mail, Excite, FastMail, Gmail, GMX Mail, Hushmail, iCloud[a], Laposte.net, Lycos, Mail.com, Mail.ru, Mailfence, Outlook.com, ProtonMail, Rackspace, Rediffmail, Runbox, Tutanota, Yahoo! Mail, Yandex Mail, Zoho Mail
E.g. When choosing a gmail id: Username Length should be 6 - 30 charactersUsername should not contain &=_'-+,<>Username cannot start or end with special charactersusername cannot contain two consecutive special characters (e.g. .. not allowed but a.1.c is allowed)
Is there anyway we can find these.
I tried to find by creating a username in some of the providers. Some providers are very cryptic in error messages to understand.
Asking here as a final resort
