Verify Email Tool first checks if a given email address is in the correct format. Second, it verifies if the domain is accepting email and if the mailbox specified is available. It can also be used to check if mail server has been properly configured in DNS.
Is it safe to assume mailbox exists if this tool returns OK?
In the majority of cases yes. Any RFC complaint mail server will reject a mail message if a mailbox is unavailable. Only a few mail servers accept all email and don't indicate absence of a mailbox.
What is catchall mail server?
Some mail servers are configured to accept all emails for the domain - even if the mailbox specified is not available. Such mail servers are marked catch all.
Does this tool send a real email message?
No, we don't spam. This tool just connects to the mail server and will not send any email messsages.