Accuracy concerns with Mailgun's email verification service

[FlyingEagle]

I’m working on implementing email verification for our newsletter subscription system. We want to validate email addresses right when users sign up, before storing them in our database.

I’m considering using Mailgun’s email validation API for this purpose. However, I’m worried about potential accuracy issues. Can this validation system incorrectly mark valid email addresses as invalid? Has anyone experienced situations where legitimate emails get flagged as bad?

Also, I’m curious about Mailgun’s behavior during actual email delivery. If we somehow end up with a previously flagged email in our system, does Mailgun perform another validation check before attempting delivery? Or will it still try to send the email regardless of previous validation results?

Any insights from developers who have used this service would be really helpful.

[Alex_Brave]

i’ve been using Mailgun validation for 8 months - it definitely has quirks. biggest issue i see is .edu emails getting flagged as risky when they’re perfectly valid. international domains also get weird false positives. for delivery: Mailgun keeps validation & sending separate. once sent, it won’t recheck validation - just tries to deliver regardless.

[Hermione_Book]

I’ve used Mailgun’s validation API for two years across several projects. It’s pretty accurate, but you’ll get false positives about 2-3% of the time. Usually happens with newer domains or corporate emails that have aggressive spam filters - the API gets too cautious. Here’s something important: Mailgun doesn’t re-validate during actual sending. If an email’s in your system and you send via SMTP or API, they’ll try to deliver it no matter what the validation said earlier. The validation and delivery are totally separate. One tip I learned the hard way - don’t use validation as a hard block. I flag sketchy addresses for manual review instead of auto-rejecting them. Saved me from losing legit subscribers.

[DancingBird]

I run a SaaS with about 50k email validations monthly through Mailgun. It works pretty well but has some quirks. The biggest issue? Catch-all domains. Valid addresses often get marked as ‘unknown’ because Mailgun can’t tell if the mailbox actually exists. Corporate emails are another pain point - their security setups block validation queries, so you get false negatives. Here’s something weird: validation and sending don’t talk to each other at all. I’ve had emails marked invalid during validation that delivered just fine later. Mailgun will happily try sending to addresses it previously flagged as bad. Now I treat validation results as suggestions, not rules. For high-value signups, manual verification is often worth the extra work.