[amaurymartiny]

During the pandemic, I launched [link redacted], an open-source tool to check if an email exists, without sending any email. Not sure what "successful" means here, but I have a couple dozens of customers, which for me is a success.

[gnicholas]

I'll definitely check this out. This would make it easier to move things from LinkedIn messaging (super annoying and low-frequency for many people) to email. There used to be a Chrome extension that made this possible (Rapportive?), but I think they got acquired by LI. Are there other efficient ways of doing this? I'm not looking to spam strangers — just to migrate conversations with actual connections off the LI platform.

[node-bayarea]

Very cool! How does this actually check without sending any email?

[biot]

From the GitHub source, it connects to the mail server for the domain’s MX record and issues a “RCPT TO:” command and looks for a non-rejection. Back when I was managing email servers, this option was typically disabled to prevent address enumeration and I’d be surprised if it still works reliably.

Many mail servers function by answering all “RCPT TO:” commands (for the domains served) with a success message that is effectively “Yeah, sure... give it a try” and, if the mailbox doesn’t exist, will email the sender a bounce message.

[meowster]

You can initiate a connection with the mail server, and then query it. I read about it years ago, never done it myself though.

[snowwrestler]

Worth pointing out that it’s possible to configure an email server to not respond to these types of queries and many high-value targets (large corporate email systems) do.