NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Email Verification on Google Sheets - An add-on for email verification directly in Google Sheets
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
Sheetlist - Discover free Google Sheets for marketing, finance and more
DeBounce - Email Validation, Email Checker, Data Enrichment and Appending Tool. Using DeBounce remove invalid, disposable, spam-trap, syntax and deactivated emails.
Clearbit Salesforce Prospector - Quickly build targeted lead lists directly in Salesforce