It takes time to check out new user registrations with such services as cleantalk.org. When a particular mailserver domain produces user registrations that have to be deleted time after time because the users have spammed other sites, that domain has to go. Here is a current list of banned domains and e-mails. My apologies if yours has been included and you are not a spammer. Getting your own domain name for just e-mail can be as cheap as $10/year. Please try that.
Banned Domains & E-Mail Addresses
@yahoo.com
@spamavert.com
@price.zonerig.com
@what.harboxed.com
@rng.emific.com
@posh.hammerwin.com
@buy.hammerwin.com
@singonline.net
@freecontests.xyz
thomasnthompson@outlook.com
@mail.ru