Several SMTP extensions are widely used in email marketing:
SIZE: This extension allows the sender to declare the size of the email message, ensuring that the recipient's server can handle it. STARTTLS: This extension upgrades a plain text connection to an encrypted one, enhancing the security of email transmissions. AUTH: This extension enables authentication mechanisms, such as plain text, CRAM-MD5, and others, to verify the sender's identity. PIPELINING: This extension allows multiple SMTP commands to be sent in a single network round trip, improving the efficiency and speed of email transmission. DSN (Delivery Status Notification): This extension provides detailed delivery notifications, helping marketers track the status of their emails. 8BITMIME: This extension allows the transmission of 8-bit MIME (Multipurpose Internet Mail Extensions) data, useful for sending multimedia content without encoding.