Direct answer
Use format checks, optional domain or disposable checks, bot controls and confirmation messages. A verifier helps reduce mistakes but cannot prove the registrant controls the inbox.
More questions and answers
Can I check an email before someone clicks submit?
Yes, if your chosen verification provider offers an API and the form handles latency and uncertainty. Verify the exact integration feature before promising it to users.
Why do I get signups with mailinator addresses?
Temporary-mail services are often used for one-time registrations. Decide whether that is acceptable for your service and flag disposable domains where a lasting address is needed.
How do I stop people entering gmial.com in a form?
Show a suggested correction for likely provider typos and let the user confirm it. Silent rewriting could send sensitive mail to the wrong destination.
Do I still need double opt-in if the email verifies?
Verification checks an address; confirmed opt-in establishes that someone with inbox access clicked the confirmation link and helps document interest. They solve different problems.
How do I reject invalid emails without blocking good customers?
Distinguish clearly invalid syntax from uncertain server checks, give users a correction path and avoid hard-blocking every catch-all or unknown result.