If an account is seen to be using a "disposable email account" then the account is likely to be removed.
We appreciate they can be useful to avoid spam when signing up for services you are unfamiliar with, but it is also often a strong indicator of the site terms of service not being adhered too. (Multi accounts, for example)
For me, this is most obvious when a high rated player loses to a provisional player. The provisional account shoots up to 3000 in one game, is undefeated until the provisional rating matures, and then crashes out to another provisional player, where the process is repeated.
In reality, players over 2100 don't play provisional players, there is absolutely nothing in it for them. If they win, they gain no rating at all, if they lose, it is to a 1200 rated player who is obviously pretty strong.
Are you able to create any stats about live games between players of a certain rating? I would red flag any open invite game played between a 2100+ and a p1200 (possibly even expand that to any provisional rated opponents full stop, depending on numbers). I would hazard a guess that 90% of the games (at least) would be multi-accounts.
Either that or do a check on 2100+ rated accounts that regularly play provisional accounts. One or two games, if you have a friend who has just joined or something, fair enough. If someone gets to 2599 (for example) by playing 15 move walkovers against 2200 opposition, then it should be pretty obvious that they are cheating..