How e mails are sent in mail server back end
Here's a high-level overview of how emails are sent in a mail server backend:
Step 1: User Composes an Email
A user composes an email using a mail client (e.g., Gmail, Outlook, etc.) and sends it to the mail server.
Step 2: Mail Server Receives the Email
The mail server receives the email from the user's mail client and stores it in a temporary queue.
Step 3: Authentication and Authorization
The mail server authenticates the user's credentials (e.g., username and password) and checks if the user has the necessary permissions to send emails.
Step 4: Email Processing
The mail server processes the email, which includes:
- Checking the email's validity (e.g., checking for viruses, spam filters)
- Verifying the recipient's email address
- Adding headers and footers to the email (e.g., sender's email address, subject line)
- Encrypting the email (if necessary)
Step 5: DNS Lookup
The mail server performs a DNS (Domain Name System) lookup to resolve the recipient's email address to an IP address. This is done to determine the mail server responsible for delivering the email.
Step 6: Mail Server Connection
The mail server establishes a connection to the recipient's mail server using the IP address obtained from the DNS lookup.
Step 7: Email Transfer
The mail server transfers the email to the recipient's mail server using a protocol such as SMTP (Simple Mail Transfer Protocol) or ESMTP (Extended SMTP).
Step 8: Email Delivery
The recipient's mail server receives the email and stores it in the recipient's mailbox.
Step 9: Email Retrieval
The recipient retrieves the email from their mailbox using their mail client.
Here's a more detailed look at the SMTP protocol, which is used to transfer emails between mail servers:
- SMTP Connection: The mail server establishes a connection to the recipient's mail server using the SMTP protocol.
- HELO/EHLO Command: The mail server sends a HELO (Hello) or EHLO (Extended Hello) command to the recipient's mail server to introduce itself and negotiate the SMTP session.
- MAIL FROM Command: The mail server sends a MAIL FROM command to specify the sender's email address.
- RCPT TO Command: The mail server sends a RCPT TO command to specify the recipient's email address.
- DATA Command: The mail server sends a DATA command to send the email content.
- QUIT Command: The mail server sends a QUIT command to terminate the SMTP session.
This is a simplified overview of the email sending process in a mail server backend. There are many other details and nuances involved, but this should give you a good starting point for understanding the basics!