Hi, we are https://mailcheck.co - SaaS service whose mission is to help marketers to avoid mail delivery caveats.

We do email list verification, by ranking mails. We can split mostly good mailboxes from ones that will bounce.

We use standard methods, like SMTP checks etc, but main our difference is our external services proofing. We check is observed mail used for registration in LinkedIn or GitHub. If yes - it's almost always working mail. Also we could provide some additional info about mailbox owner ;)