Email sandbox
On this page
Viewing messages
Click a message in the list to open it. The viewer has a tab for each way of looking at it.
| Tab | Shows |
|---|---|
| HTML | The HTML body, rendered in a sandboxed frame. Switch between phone, tablet and desktop widths to catch layout bugs. |
| Text | The plain-text part, as recipients without HTML see it. |
| Raw | The original MIME source, exactly as received. Download saves it as an .eml file you can open in any mail client. |
| Headers | Every header in its original order: Message-ID, List-Unsubscribe, DKIM signatures, custom X- headers. |
| Spam & placement | A spam score, an inbox-placement estimate, the rules that fired with fixes, and the Gmail/Yahoo sender checklist. |
| Check | Which HTML and CSS features in the message popular email clients do not support. |
Attachments are listed under the message and always download (they are never opened inside the app). Inline images referenced with cid: are shown in the HTML preview.
Spam analysis
When the server is connected to SpamAssassin (spamd), the Spam tab shows SpamAssassin's score against its threshold, and every rule that fired with its points and description. Without spamd, Testlie runs built-in heuristics (missing From, Date or Message-ID, an HTML body without a plain-text part, all-caps or over-punctuated subjects, common spam phrases, a high image-to-text ratio, images without alt, <script>, <form> or <iframe> in the HTML, and HTML over Gmail's 102 KB clipping limit) so you still get a useful signal. The result is cached with the message, so opening it again is instant.
Use it to catch problems before real mail providers do: a high score in staging usually means the same email would land in junk folders in production. The tab also estimates inbox placement, explains how to fix each rule and checks the Gmail and Yahoo bulk-sender requirements; see Spam reports & failure scenarios.
HTML compatibility check
The Check tab parses the message's HTML and CSS and compares every element, attribute and property it uses against the caniemail.com support data for popular clients (Gmail, Outlook, Apple Mail, Yahoo and others). It shows an overall support score, a score per client, and each unsupported or partially supported feature with the clients affected and links to the details, so you can decide whether it matters for your audience.
Search and unread
The search box matches subject, sender and recipients. Unread only filters the list, and Mark all read clears the unread counts for everyone on the team. Empty inbox deletes every message in it.
Privacy of previews
The HTML preview cannot run scripts: it is served with a Content-Security-Policy that sandboxes the document and blocks scripts, and it is shown in a sandboxed iframe. On servers configured with a separate user-content domain, previews load from that domain, so message HTML never runs on the app's origin. When the image proxy is on (the default for the hosted service), remote images and stylesheets load through Testlie, so opening a message does not reveal your IP address or browser to whoever sent it and tracking pixels only see the proxy.
Forwarding a message
To see a message in a real mail client, use Forward on the message to send it to a verified forwarding address.