Antivirus blocks the bridge (Windows)

In short: some security tools — Malwarebytes Premium is the one we’ve seen — block Thunderbird from starting other programs and may quarantine atbridge.exe. Check the file is genuine, allow that one file, install from your own PowerShell window, then run atbridge bridge install --windows-launcher=exe so Thunderbird starts atbridge directly. You don’t need to turn protection off.

What you might see

• Exploit.EmailClientScriptingAbuse (Malwarebytes, Application Behavior Protection, affected application: Thunderbird) — blocking powershell.exe during setup, or cmd.exe … bridge-host.bat every time Thunderbird starts.
• Malware.AI.<number> — atbridge.exe moved to quarantine.
• The @bridge setup wizard keeps saying the bridge is not connected, even after atbridge bridge install succeeded.

Why this happens

There are two separate detections:

1. Thunderbird starting a script. The wizard’s one-click Install button has Thunderbird start PowerShell to run the installer. And by default, Thunderbird starts the atbridge bridge through a small bridge-host.bat file, which Windows runs with cmd.exe. Some security tools block any email program from starting PowerShell or cmd.exe, because that’s a common trick in malicious attachments. It’s a sensible rule — it just also catches atbridge.
2. The program file itself. Malware.AI is a machine-learning guess, not a known-malware signature. It sometimes flags new Windows programs that don’t carry a code-signing certificate, and atbridge doesn’t have one yet.

Fix it

1. Check the file is genuine. In PowerShell:

   Get-FileHash "$env:USERPROFILE\.atbridge\bin\atbridge.exe"

   Compare the hash with the atbridge-windows-amd64.exe entry (or atbridge-windows-arm64.exe on ARM) in atbridge.ai/download/latest.json. If they match, it’s the official build. (For a cryptographic check, every release also has a minisign signature — see Verify a download below.)

2. Restore and allow that one file. If your security tool quarantined atbridge.exe, restore it and add that single file to the tool’s allow list. In Malwarebytes both are under Detection History (the Quarantine and Allow List tabs).

3. Install from your own PowerShell window, not the wizard’s one-click button. Open PowerShell from the Start menu and run:

   irm https://atbridge.ai/install.ps1 | iex

   PowerShell started by you isn’t an email program starting a script, so the rule doesn’t fire. Already installed? Skip this step.

4. Let Thunderbird start atbridge.exe directly — no .bat, no cmd.exe:

   atbridge update
   atbridge bridge install --windows-launcher=exe

   If the second command says unknown flag: --windows-launcher, your atbridge is older than this option — run atbridge update again (or re-run the install command from step 3), then retry.

5. Restart Thunderbird completely (close every window), then check:

   atbridge bridge ping

   Connection OK means the bridge is working. Go back to the setup wizard to finish activation.

Caution

Allow only atbridge.exe — don’t exclude whole folders, and don’t turn off exploit or behavior protection. Those settings protect you from real attacks; none of the steps above needs them off.

Undo the launcher change

To go back to the original .bat launcher:

atbridge bridge install --windows-launcher=bat

Then restart Thunderbird. Updates keep whichever launcher you chose.

Verify a download with minisign

Download the signature next to the file and check it with minisign:

Invoke-WebRequest https://atbridge.ai/download/atbridge-windows-amd64.exe.minisig -OutFile atbridge.exe.minisig
minisign -Vm "$env:USERPROFILE\.atbridge\bin\atbridge.exe" -x atbridge.exe.minisig -P RWRcsvLUnunMtkopNcGmMWsCCp1ADHB2qUb0JTvKU8rdyFohUN34bU5z

Signature and comment signature verified means the file is exactly what we published. The install script runs this same check automatically when minisign is installed.

Still not connecting?

Run atbridge bridge ping and atbridge bridge install and send us the output — along with your security tool’s detection name — through the help form on Install atbridge. If the block is from a different product, the detection name tells us which rule to look at.

Where to go next

• Windows blocks the app (SmartScreen)
• Install atbridge
• When your AI can’t find anything

Faster: ask the community

For “how do I…” questions you will usually get a quicker answer — and help the next person with the same question — in Discord. Anything tied to your account, billing, or a bug is better as a support ticket, where we reply by email.