Definition
Multipart (or MIME multipart) is the structure of an email that contains more than one version of its content — typically an HTML version and a plain-text fallback — combined into a single message. Receiving clients display the version they support, which makes the email readable across virtually all environments.
This approach is important for deliverability and compatibility. Some clients and security filters prefer or require a plain-text part. Providing both means no recipient is left with broken or unreadable content.
How Multipart Builds an Email
| Part | Purpose |
|---|---|
| HTML part | Rich, styled version for capable clients |
| Plain-text part | Simple version as fallback |
| MIME boundaries | Separators between the parts |
Both parts travel in one message and the client picks the best fit.
Why Multipart Matters
- Broad compatibility: Works in clients without full HTML rendering.
- Better deliverability: Filters value a plain-text alternative.
- Accessibility: Plain text reads well in screen readers and limited devices.
- Fallback safety: Recipients without HTML support still see readable content.
How to Send Multipart Email
- Set both parts: Include an HTML and a matching plain-text version.
- Keep the text meaningful: Avoid blank or robotic plain-text fallbacks.
- Test in multiple clients: Confirm the right part displays correctly.
- Let the client decide: Multipart lets each client choose its preferred version.
Related Glossary Terms
Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
Alt Text
Alt text is the written alternative to an image in an email, displayed when images are blocked, slow to load, or consumed by screen readers.
AOL Mail for Email Marketers
AOL Mail is a legacy email provider with specific deliverability requirements and rendering quirks, now operating as part of the Yahoo+AOL network under shared infrastructure.
Email Authentication Protocols
Email authentication protocols are technical standards that verify the identity of an email sender, helping mailbox providers distinguish legitimate mail from spam and phishing.
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Management
Bounce management is the process of handling emails that are rejected by mailbox providers, including classification, removal of bad addresses and protection of sender reputation.
Frequently Asked Questions
A multipart email carries more than one version of its content, typically an HTML version and a plain-text version, together in a single message. The client displays whichever version it supports.
A plain-text fallback ensures the email is readable in clients that cannot render HTML, improves accessibility, and can help with deliverability and filters that expect a text alternative. It protects against broken displays.
Yes, in a positive way. Many filters and environments value a plain-text alternative, so sending both parts can support inbox placement while ensuring a readable fallback regardless of the recipient's client.
A HTML-only email contains a single rich version and may render poorly or fail in limited clients. A multipart email includes both HTML and plain text, so every client receives a supported format and the content stays readable.