What is Simple Mail Transfer Protocol (SMTP)?
SMTP (Simple Mail Transfer Protocol) is the standard language used by computers to send emails across the internet.Think of it as the digital postal service. While other protocols are responsible for receiving mail, SMTP is the mail carrier that picks up your letter and delivers it to the recipient's post office.
How SMTP Works
When you hit "Send", your email doesn't just fly directly to the recipient's inbox. It goes through a series of handshakes between servers.- Submission: Your email client (like Outlook or Gmail) connects to your configured SMTP server.
- Handshake: The client and server identify themselves and verify that the sender is authorized to send mail.
- Routing: The SMTP server looks at the domain of the recipient (e.g., @gmail.com) and finds the destination server.
- Transfer: The servers communicate using SMTP commands to move the data.
- Delivery: The email is dropped off at the recipient’s server, where it stays until the recipient downloads it.
Key SMTP Components
To keep the mail moving, SMTP relies on several "agents":- MUA (Mail User Agent): This is your email app (Gmail, Apple Mail).
- MSA (Mail Submission Agent): Receives the email from the MUA and checks for errors.
- MTA (Mail Transfer Agent): The "sorting office" that routes the mail to the right destination.
- MDA (Mail Delivery Agent): Delivers the mail into the recipient's actual mailbox.
Common SMTP Ports
Servers use specific "doors" (ports) to communicate. Depending on security needs, you'll usually see one of these:- Port 25: The original, but now mostly used for server-to-server communication (often blocked by ISPs for security).
- Port 587: The modern standard for email submission, usually paired with encryption (TLS).
- Port 465: Originally for "SMTPS", now used by some older systems for secure connections.
SMTP and MIDAS
MIDAS supports sending email via an SMTP server or relay in both cloud and self hosted editions. Other available email sending options are Sendmail (for self hosted editions of MIDAS) and "Cloud" (for cloud hosted editions of MIDAS from v4.42).