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V4 Contacts Checker

Checks whether email addresses in your Thunderbird messages are already leads in V4 Contacts, shows each lead's live status, and lets you jump straight to the right next action in v4.vdm-vsg.de.

Download latest
Current version: latest
Tip: save the file — don't open it in the browser.
How to install (about 2 minutes)
1

Download the add-on

Click Download latest above and save v4_contacts-latest.xpi somewhere you can find it (e.g. Downloads).

2

Get your V4 API key

Open v4.vdm-vsg.de, go to Account, and copy the API key shown below your signatures. Keep it handy — you'll paste it in step 5.

Copy the API key from your V4 Account page Add docs/images/key-account.png
V4 → Account → the API key under your signatures.
3

Allow internal add-ons (one-time)

This add-on is distributed internally, so it isn't signed by the public add-on store. You only need to do this once.

It only affects unsigned installs; signed add-ons still work as before.
Open Thunderbird Settings Add docs/images/allow-settings.png
a. Thunderbird menu → Settings (on Windows/Linux: the ☰ menu).
Open the Config Editor Add docs/images/allow-config.png
b. General → scroll to the bottom → Config Editor… (accept the warning).
Set xpinstall.signatures.required to false Add docs/images/allow-false.png
c. Search signatures.required → double-click xpinstall.signatures.required so it reads false.
4

Install from file

Open Add-ons and Themes Add docs/images/install-addons.png
a. Tools menu → Add-ons and Themes.
Install Add-on From File Add docs/images/install-fromfile.png
b. Gear ⚙ (top-right) → Install Add-on From File… → choose the .xpi you downloaded → confirm Add.
5

Paste your API key

Open Add-ons and Themes → V4 Contacts Checker → Preferences, paste the API key you copied in step 2, and click Save.

You also need to be logged into v4.vdm-vsg.de in your browser for the Mark buttons to open the right lead.

Paste the API key in Preferences Add docs/images/key-paste.png
The add-on's Preferences tab, with the API-key field.
That's it. From now on Thunderbird checks for new versions automatically and updates in the background — you won't need this page again unless you reinstall.