`MIMEMultipart("alternative")` — for HTML + plain text (same content, different formats) - `MIMEMultipart("mixed")` — for email + attachments - `MIMEMultipart("related")` — for HTML + inline images - `MIMEText(body, "plain")` — plain text body part - `MIMEText(html, "html")` — HTML body part - `MIME