Disposable email dies at the MX record, not the signup form

Sites don't block temp-mail addresses by maintaining domain blocklists by hand — they check the MX records and domain reputation at signup. A disposable provider's domains all route to the same mail infrastructure, so one lookup classifies every domain the service will ever register. That's why "they blocked domain X, I'll use their domain Y" rarely works: Y resolves to the same MX.

The corollary: temp mail works fine on services that only need delivery (newsletters, download gates, one-off verifications) and fails systematically on services that check reputation (financial, major platforms, anything with fraud exposure). It's not randomness — it's whether the signup flow does the lookup.

For the second category the workable option isn't a better disposable domain; it's an alias on a real mailbox (plus-addressing or a masking service), which passes MX checks because it is real mail.

Providers compared by what they actually pass: https://toolfreebie.com/free-temp-email-services/