Email Verification on Google Sheets - An add-on for email verification directly in Google Sheets
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Sheetlist - Discover free Google Sheets for marketing, finance and more
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
Clearbit Salesforce Prospector - Quickly build targeted lead lists directly in Salesforce
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.