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Disposable email services let bad actors sail past basic format validation. Here's how domain block-lists, MX checks, and rate limiting help — and where they fall short.
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Disposable email addresses can't be caught by format validation alone since they look like normal addresses. The common techniques are checking the domain against a known block-list of disposable providers, verifying the domain actually has valid mail servers via its MX records, and rate limiting signups by IP address to slow down bulk abuse.
A regular expression that checks for a valid email shape will happily pass realuser@10minutemail.com. It's a well-formed address that receives mail for exactly as long as the sender needs it to — long enough to confirm a signup, claim a trial, or leave a submission with no way to follow up. Format validation was never designed to catch this, because the problem isn't the string, it's the domain behind it.
Domain block-lists. The most direct approach: maintain (or subscribe to) a list of known disposable-email domains and reject signups from any of them. This works well against popular, long-lived services, but it's a losing arms race against new disposable domains that spin up constantly — a list is only as good as how often it's updated.
MX record checks. Every domain that can actually receive mail publishes DNS records (MX records) pointing to its mail servers. Checking that a submitted domain has valid MX records filters out typos and completely fake domains, though it does nothing to catch a disposable service, since those domains have perfectly valid mail servers too — that's the whole point of the service.
Rate limiting by IP. Disposable-email abuse is often paired with volume — one actor creating many signups quickly. Limiting how many submissions a single IP address can make in a given window doesn't identify disposable emails directly, but it caps the damage of automated abuse regardless of which technique the abuser is using to get past your form.
In practice, teams that care about this combine two or three of these rather than relying on one, since each has a different blind spot.
FormBridge doesn't currently include a dedicated disposable-email block-list. What it does have are two features that act as partial, general-purpose mitigations depending on your situation:
If disposable-email abuse specifically is a real problem for your signup flow, pairing FormBridge's built-in layers with your own domain block-list check (run before or after the submission, depending on your setup) covers more ground than either alone.
Format validation only checks that a string looks like an email address (has an @ symbol, a domain, and so on). A disposable address like someone@10minutemail.com is a perfectly valid email format — the problem is the domain, not the syntax, so catching it requires checking against a list of known disposable providers or the domain's actual mail infrastructure.
FormBridge doesn't have a dedicated disposable-email block-list feature. It does offer authorized domains, an allow-list restricting which domains a form can accept submissions from, and automatic spam scoring on every submission before it reaches your inbox — both of which act as partial mitigations depending on your setup.
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