What this checks
It validates the address format and looks up the domain's MX records — the servers that accept mail for it. A domain with no MX (and no A record) will bounce every message.
Why it matters for cold email
Sending to dead or malformed addresses drives up your bounce rate, one of the fastest ways to wreck a sending reputation and land in spam. leads2mail runs this exact MX + syntax check before every campaign.
Honest note: This is an MX + syntax check. It does not open an SMTP session to confirm the individual mailbox exists — that is unreliable and hurts reputation — so a “looks deliverable” result is not a 100% guarantee.