Definition
A multipart email uses the MIME (Multipurpose Internet Mail Extensions) standard to include multiple versions of the same message in a single email — typically an HTML version and a plain-text version. When the email is delivered, the email client selects the version it supports best: HTML-capable clients display the rich HTML version; limited clients display the plain-text version.
Multipart encoding is standard practice for email marketing. Every professional ESP automatically creates multipart messages, combining the HTML email you design with an auto-generated plain-text alternative. Ensuring the plain-text version is meaningful — not just auto-stripped HTML tags — is an important best practice.
Why Multipart Matters
| Reason | Detail |
|---|---|
| Deliverability | Spam filters favour emails with both HTML and plain-text parts |
| Accessibility | Plain text is readable by screen readers for visually impaired recipients |
| Client compatibility | Some mobile clients and limited email clients show plain text only |
| Security | Plain text cannot hide malicious links or content |
| User preference | Some recipients prefer reading plain-text emails |
Best Practices
- Review your plain-text version before every send — do not rely on auto-generation
- Format plain-text emails with line breaks, bullet characters, and readable link URLs
- Ensure all links in the plain-text version are full URLs (not raw HTML)
- Include unsubscribe instructions in the plain-text version
- Test both versions to verify they convey the same message
- Use a plain-text editor to manually craft important campaign plain-text versions
- Maintain consistent messaging between HTML and plain-text versions
Related Glossary Terms
Frequently Asked Questions
Yes — positively. Emails with both HTML and plain-text MIME parts are treated as more legitimate by spam filters. Spam messages are often HTML-only. A plain-text part signals that the sender follows email standards and cares about accessibility.
Your ESP likely auto-generates a plain-text version by stripping HTML tags. However, auto-generated plain text is often unreadable. Manually review and edit the plain-text version for each campaign: format with line breaks, use simple bullet characters, include full URLs for links, and verify the unsubscribe mechanism is clear.