VeriMails

The list has the right person at the right company, and one empty column: the email address. A guessed address like firstname@company.com may reach nobody. VeriMails looks up the address from a first name, last name and company domain. It returns a result only once a check confirms that the mailbox exists.

Addresses you already have get the same live check with the receiving mail server. Each result carries a "safe to send" flag, set only for a confirmed mailbox that can receive mail. Some company domains accept mail for any address, so a check there cannot tell a real inbox from an invented one. These catch-all domains go into a separate group, which the guide suggests keeping out of large sends.

Bulk checks take a CSV file and return it with every original column kept and the results added. The homepage gives 20 to 40 minutes for a list of 10,000 addresses. Signup forms and in-house software can call a REST API with one address or a batch, and a webhook tells your system when the batch is done.