Install in Yahoo Mail, Mozilla Thunderbird & Custom Webmail
How to install your HTML email signature into Yahoo Mail, Mozilla Thunderbird, ProtonMail, and cPanel Roundcube webmail without broken tables.
Overview
While Gmail and Outlook dominate the corporate market, millions of professionals and agencies rely on independent email clients: Yahoo Mail for business, Mozilla Thunderbird for Linux/privacy workflows, ProtonMail for encrypted communications, and cPanel Roundcube for custom domain webmail.
Because Sig Signature compiles to 100% inline CSS and standard HTML tables, your signature integrates seamlessly into every platform.
1. Installing in Yahoo Mail (Web)
Copy Visual Signature
Open your signature in Sig Signature and click Copy Visual Signature.
Open Yahoo Mail
Log into Yahoo Mail in your web browser.
Open More Settings
In the top right corner, click Settings → Click More Settings at the bottom of the tray.
Navigate to Writing Email
In the left navigation, click Writing email.
Enable Signature
Under Signature, toggle your account signature ON.
Paste Visual Signature
Click inside the text box, press Ctrl+V (Windows) or Cmd+V (Mac) to paste your visual signature.
Verify Display
Changes in Yahoo Mail save automatically. Compose a new message to verify the visual display.
2. Installing in Mozilla Thunderbird (Desktop)
Thunderbird supports direct HTML source embedding, guaranteeing pixel-perfect results:
Method A
HTML File Attachment (Recommended)
- In Sig Signature, click Export HTML → Click Download .html File. Save it to a permanent folder on your computer.
- Open Thunderbird.
- Right-click your email account in the left sidebar → Select Settings.
- In the main Account Settings panel, check the box labeled:
- "Attach the signature from a file instead (text, HTML, or image)".
- Click Choose..., select your downloaded signature.html file, and click Open.
- Click OK. Thunderbird will now render your HTML signature natively in every outgoing message.
Method B
Direct HTML Source Paste
- In Sig Signature, click Export HTML → Copy Raw HTML.
- In Thunderbird Account Settings, check the box "Use HTML" in the Signature text section.
- Paste your raw HTML code directly into the text box.
3. Installing in ProtonMail
Copy Visual Signature
In Sig Signature, click Copy Visual Signature.
Open ProtonMail Settings
Open ProtonMail Web → Click Settings (gear icon) → All settings.
In left navigation, click
In left navigation, click Identity and addresses.
Scroll to Signature, toggle it ON.
Paste Signature
In the rich-text editor, paste your signature (Ctrl+V or Cmd+V).
Save Configuration
Click Save.
4. Installing in cPanel Webmail (Roundcube)
Copy Raw HTML
In Sig Signature, click Export HTML → Copy Raw HTML.
Open Roundcube Webmail
Log into your cPanel Webmail and open Roundcube.
Open Identities Settings
In the top-right menu, click Settings → Click Identities in the left column.
Select Email Identity
Select your email identity.
Enable HTML Signature
In the right-hand panel, check the box HTML signature.
Open HTML Source Editor
In the signature editor toolbar, click the HTML Source Code icon (< >).
Paste HTML Code
Paste your raw HTML code into the popup window and click Update.
Save Configuration
Click Save.
Diagnostic Checklist & Reference
| Client | Paste Method | Notes |
|---|---|---|
| Yahoo Mail Web | Copy Visual Signature | Rich text paste; auto-saved in settings |
| Mozilla Thunderbird | Attach HTML File or Raw Code | Supports full HTML markup without sanitization |
| ProtonMail | Copy Visual Signature | E2E encrypted; images load via Proton proxy |
| Roundcube / cPanel | Copy Raw HTML Code | Must enable the HTML signature toggle |
Key Takeaways
- Thunderbird and Roundcube support direct raw HTML pasting via their code view tools.
- Yahoo Mail and ProtonMail require copying the "Visual Signature" directly to clipboard.
- All signatures render consistently because Sig Signature avoids unsupported external styles.