Webinar and Event Registrants: How to Verify Emails and Phone Numbers Before Reminders Go Out

Why registrant lists bounce more than you'd expect

A registration form is a quick, low-commitment step, so it collects lower-quality data than a purchase:

• Typos. Registrations on a phone keyboard produce gmial.com and missing letters, and nobody notices until the join link doesn't arrive.
• Throwaway addresses. Some people only want the recording link or the slide deck and use a disposable inbox.
• Fake entries. Required phone fields get 555-555-5555. Bots fill open forms.
• Old work emails. Browser autofill puts in an address from a previous job.

Then the reminder sequence multiplies the damage: confirmation, a week before, a day before, an hour before, "we're live", and the replay. Each invalid address can bounce on every one of them. Bounce spikes in a short window are exactly what mailbox providers and your email platform react to, and webinar reminders often go from the same domain as your main marketing.

Step 1: export registrants

Get the registrant list out of your webinar or event platform as CSV. Free browser tools that pull the email (and phone) columns out of the common exports:

• Zoom attendee report to email list
• Webinar registrants to email list
• Eventbrite attendees to email list
• Luma guests to email list, Cvent attendees and Whova attendees

Step-by-step export guides: export webinar registrants and export Eventbrite attendees.

Step 2: verify before the first reminder

Upload the export to the verify page. SimpleVerifier runs a live SMTP mailbox check on every address, asking the receiving server whether the mailbox exists without sending an email, and returns:

Result	For reminders	For post-event sales follow-up
Valid	Send	Send
Invalid	Suppress	Suppress
Risky: catch-all	Send, it's one event	Send the higher-likelihood ones; watch bounces
Risky: full or disabled inbox	Suppress	Suppress
Unknown	Send, re-check later	Re-check first

Catch-all domains accept mail for any address, so a mailbox check can't confirm the person. SimpleVerifier reports them as risky, never guessed valid, with a likelihood grade (catch-all grading). Company registrants are where you'll see most of them.

For a big event with registrations flowing in for weeks, verify in batches (every few days) instead of once, or check each registration as it arrives with the API or a Zapier step.

Step 3: fix what you can instead of deleting it

An invalid registrant may still be a real person who wants to attend. Before suppressing:

• Run the invalid rows through the email typo corrector. A corrected @gmail.com address is worth re-checking.
• If the registrant gave a phone number and opted in to texts, send the join link by SMS instead.

Step 4: SMS reminders done properly

Text reminders get seen, which is why event teams use them. They also come with rules:

1. Consent. Only text registrants who ticked an SMS opt-in. In the US, the TCPA generally requires prior consent for automated texts, and 10DLC registration asks how you collect it. The SMS compliance message generator drafts opt-in and opt-out wording.
2. Format. Registration forms accept any format. Convert numbers to E.164 (+14155552671) with the phone number formatter or the bulk phone number validator. International registrants without a country code are the usual trouble; international phone number format covers it.
3. Remove numbers that can't work. The same upload marks numbers that can't exist. The fake phone number checker flags placeholders and fictional ranges.
4. Remove landlines. In the US and Canada, only a live carrier lookup separates mobiles from landlines. Texts to landlines usually fail. See can you text a landline.
5. Keep it short. One link and the start time. The SMS character counter shows when a message spills into a second segment.

If your audience is international and prefers WhatsApp, the WhatsApp number formatter turns the same list into wa.me-ready numbers. Messaging people on WhatsApp still needs their opt-in.

Step 5: verify again before the follow-up

After the event, the list splits into attendees and no-shows, and both usually go to sales or a nurture sequence. That is a different send from a reminder: colder, more promotional, and more likely to hurt you if it bounces. Re-verify the whole list (results from two weeks ago are mostly still good, but new registrations and late changes aren't), and apply the stricter column of the table above.

Consent matters here too. A registration for a webinar isn't always consent to marketing email, especially for EU, UK and Canadian registrants. The GDPR email consent checker and the CASL consent checker help you decide per contact, and the email consent checkbox generator gives you opt-in wording for the next registration form. This isn't legal advice.

If you're sending from a new domain or IP

Big virtual events sometimes move reminders to a new sending domain or a dedicated IP so marketing reputation isn't affected. A new IP needs a gradual ramp before it can handle a full reminder blast; the IP warmup schedule calculator lays out a day-by-day plan. Send the warmup traffic to verified addresses only. Bounces during warmup do more damage than bounces on an established sender, because the receiving providers have nothing else to judge you by.

A simple schedule

When	What
Registration opens	Verify on arrival via API, or batch every few days
Day before the event	Verify anyone not yet checked; prepare SMS list
After the event	Re-verify the full list; split attendees and no-shows
Before the next event	Merge lists, dedupe, re-check anything older than a few months

What it costs

• Free: 100 checks with a Google sign-in, no card.
• Starter, $9 a month: 2,500 emails a month, fine for smaller webinars.
• Pro, $39 a month: Unlimited email verification*, phone format checks, the API and the MCP server.
• Pro + Phone, $49.99 a month: adds 5,000 live carrier lookups a month.

*Fair use: the first 100,000 checks a month at full speed, then slower, never cut off.

See pricing.

More reading: cleaning a trade show attendee list, hard bounce vs soft bounce, why SMS delivery fails.