What I Found
You can verify many email addresses without sending a test message by checking the domain's MX records and talking.
Sometimes you need to know whether an email address is real before you send anything important to it. The usual quick test is to send an email and wait to see if it bounces back, but that is not always reliable.
The practical way to check an email address from Terminal is to look up the domain's MX records, connect to one of its mail servers on port 25, start an SMTP handshake, and use the RCPT TO command to ask whether the server will accept mail for that address.
What this video covers
- Why Not Just Send a Test Email?
- Step 1: Find the Mail Server
- Step 2: Connect Over SMTP
- Step 3: Start the Handshake
- Step 4: Provide a Sender
The short version
The practical way to check an email address from Terminal is to look up the domain's MX records, connect to one of its mail servers on port 25, start an SMTP handshake, and use the RCPT TO command to ask whether the server will accept mail for that address.
