Frequently asked questions.

InboxCheck is a Chrome extension that verifies email addresses in real time. When you browse any website, InboxCheck detects email addresses on the page and adds a verify button next to each one. Clicking the button runs a full SMTP verification and returns a verdict: Safe, Risky, or Unsafe. It is designed for sales development reps, BDRs, and outbound teams who need to verify prospect emails without leaving their current page.

Visit the Chrome Web Store, search for InboxCheck, and click Add to Chrome. The installation takes about ten seconds. After installing, sign up for a free account using Google sign-in. The extension is immediately active on all websites you visit.

Yes. Every InboxCheck account includes a free daily allowance of email verifications. No credit card is required. You can sign up and start verifying immediately. If you need more verifications per day, paid plans with higher daily allowances are available starting at a few dollars per month.

InboxCheck is currently available as a Chrome extension. It works on Google Chrome and any Chromium-based browser, including Microsoft Edge, Brave, Arc, and Opera. Firefox and Safari are not currently supported.

InboxCheck runs five checks on every email address: syntax validation to catch formatting errors, DNS lookup to confirm the domain exists, MX record verification to ensure the domain has a mail server, a live SMTP handshake to confirm the specific mailbox exists and accepts mail, and disposable email filtering to catch throwaway addresses. The entire process completes in under two seconds without sending any actual email.

Safe means the mailbox exists, is active, and accepts mail. You can send to this address with confidence. Risky means the domain is a catch-all (accepts mail for any address) or the mailbox could not be definitively confirmed. Proceed with your own judgment. Unsafe means the mailbox does not exist, the domain has no mail server, or the address is a known spam trap or disposable email. Do not send to Unsafe addresses.

No. InboxCheck never sends a message to the email address being verified. The verification uses an SMTP handshake protocol, which initiates a connection to the recipient mail server, checks whether the mailbox is recognized, and then disconnects before any message is transmitted. The recipient has no way of knowing their address was checked.

A catch-all domain is configured to accept incoming mail for any address at that domain, regardless of whether a specific mailbox exists. For example, anything@catchall-company.com would be accepted by the server. This makes it impossible to verify whether a specific person's mailbox exists through SMTP checking alone. InboxCheck flags these domains as Risky so you can decide whether to include them in your outreach.

InboxCheck works on every website you visit in Chrome. The extension scans visible page content for email address patterns and adds verify buttons automatically. This includes LinkedIn, Apollo.io, ZoomInfo, HubSpot, Salesforce, company websites, Google Sheets, and any other webpage. No integration setup or API keys are required.

Email service providers like Google Workspace and Microsoft 365 track your bounce rate. If your hard bounce rate exceeds roughly 3%, your account can be throttled or suspended. For cold email campaigns built on prospect data from third-party sources, invalid rates typically range from 5% to 22% without verification. Verifying every address before sending keeps your bounce rate under 1% and protects your sender reputation.

The industry-recommended target is under 1% hard bounces. Google Workspace may flag accounts above 3%. Microsoft 365 has similar thresholds. For cold email specifically, where you are contacting people who have not opted in, maintaining a near-zero bounce rate is critical because email providers scrutinize cold outbound more closely than opted-in marketing emails.

In our 2026 Data Decay Audit, we tested 3,000 B2B emails from Apollo.io, ZoomInfo, and LinkedIn scrapers. The average invalid rate was 18.4%. LinkedIn-sourced emails had the highest failure rate at 22.5%, followed by Apollo at 14.2%. Even ZoomInfo, the best-performing provider tested, had an 8.8% combined failure rate. These results demonstrate that no data provider delivers perfectly clean data, and secondary verification is essential.

When email providers flag your domain for high bounce rates, the consequences escalate quickly. First, your outbound emails start landing in spam folders instead of the primary inbox. Then, your sending rate is throttled. In severe cases, sending is suspended entirely for 24 hours or more. Recovery requires reducing volume, sending only to confirmed contacts, and gradually warming up over several days to weeks. During recovery, your entire outbound pipeline is effectively frozen.

InboxCheck offers three plans: Solo (100 verifications per day, for individual users), Pro (500 verifications per day, for active prospectors), and Team (pooled verifications across multiple team members). All plans include the same verification technology. The difference is daily allowance volume. Annual billing saves 20% compared to monthly billing.

Burst credits are one-time credit packs you can purchase if you need additional verifications beyond your daily allowance. They never expire and are only consumed after your daily allowance is used up. Burst credits are useful for occasional high-volume days without needing to upgrade your plan permanently.

Yes. The Team plan provides a pooled daily verification allowance shared across all team members. Each team member installs the Chrome extension and signs in with their own account. The team administrator can track usage, manage members, and allocate resources from the dashboard.

No. InboxCheck does not access your email inbox, read your messages, or require any email API permissions. The extension only scans visible webpage content for email address patterns. Verification checks connect to the recipient mail server, not to your email account. Your emails and contacts remain completely private.

InboxCheck caches verification results briefly to avoid redundant checks on the same address within a short time window. Verification data is not sold, shared, or used for any purpose other than delivering results to you. Full details are available in our privacy policy.

Yes. InboxCheck processes email address verification data as a processor on behalf of the user (controller). We maintain a Data Processing Agreement (DPA) available on our website. No personal data beyond the email address being verified is processed, and verification data is not retained beyond the brief caching window.