> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lettr.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Email Content Types: HTML, Plain Text, and AMP
> When to use HTML, plain text, and AMP email content types in Lettr, what each supports, and how email clients render them.
Every email you send through Lettr contains content in one or more formats. The three supported content types are **HTML** for rich formatting, **plain text** for universal compatibility, and **AMP HTML** for interactive experiences. Understanding when and how to use each format directly affects how your emails render, how accessible they are, and how mailbox providers evaluate them.
Lettr's API accepts three corresponding parameters: `html`, `text`, and `amp_html`. At least one of `html` or `text` is required for every send.
***
## HTML Email
HTML is the most common email content format. It allows you to include styling, images, links, buttons, and structured layouts that make emails visually engaging.
### What HTML Email Supports
* Custom fonts, colors, and spacing
* Images and background images referenced from a public URL
* Clickable buttons and hyperlinks
* Multi-column layouts using tables
* Open and click tracking via tracking pixels and link wrapping
### Limitations Compared to Web HTML
HTML email is not the same as HTML on the web. Email clients strip or ignore many features that browsers handle without issue:
| Feature | Web HTML | Email HTML |
| ----------------------- | --------------- | ------------------------ |
| JavaScript | Fully supported | Completely stripped |
| External CSS (``) | Supported | Ignored by most clients |
| CSS Flexbox / Grid | Supported | Unreliable — use tables |
| `