Exchange online mail flow diagram

Here is a high-level diagram of the email flow process between two email servers:

Email Flow Diagram

Step 1: User Composes Email

User composes an email using a mail client (e.g. Outlook, Gmail, etc.)
The mail client sends the email to the user's email server (e.g. Exchange, IMAP, etc.)

Step 2: Email Server Receives Email

The email server receives the email from the user's mail client
The email server checks the email's validity and authenticity (e.g. checks the sender's IP address, checks for spam filters, etc.)

Step 3: Email Server Routes Email

The email server routes the email to the destination email server (e.g. the recipient's email server)
The email server uses DNS (Domain Name System) to look up the recipient's email server's IP address

Step 4: Destination Email Server Receives Email

The destination email server receives the email from the sender's email server
The destination email server checks the email's validity and authenticity (e.g. checks the sender's IP address, checks for spam filters, etc.)

Step 5: Email Server Delivers Email

The destination email server delivers the email to the recipient's mail client (e.g. Outlook, Gmail, etc.)
The recipient's mail client receives the email and displays it to the user

Additional Steps:

Spam Filtering: Email servers may use spam filters to check the email's content and block or quarantine spam emails
Authentication: Email servers may use authentication protocols (e.g. SMTP AUTH, OAuth) to verify the sender's identity
Encryption: Email servers may use encryption protocols (e.g. TLS, SSL) to secure the email transmission

Here is a more detailed diagram of the email flow process between two email servers:

Email Flow Diagram (Detailed)