Is mail.com MailCheck safe?

Medium risk

mail.com MailCheck embeds reusable OAuth client credentials and sends them in token requests for GMX, mail.com, and web.de accounts.

The extension ships Basic OAuth client credentials for GMX, GMX.com, mail.com, and web.de inside its bundle. During password or refresh-token OAuth exchanges, it places the configured Basic credential in the Authorization header sent to the provider token service.

Part of this rating comes from analysis signals we haven't published as detailed findings yet.

1&1 Mail & Media GmbHv8.0.20Firefox Add-ons
42Risk
Who publishes it

1&1 Mail & Media GmbH - no other listings under this identity, 31 shared hostnames

What this publisher told the store about itself, and the other listings that told it the same thing.

Publisher
1&1 Mail & Media GmbH

Shared hosts - 31 hostnames

Hostnames hardcoded in this extension that few other listings call. That can mean one operator behind both, and it can equally mean a small shared vendor, so it is context rather than a conclusion. Hosts that many listings call are left out: they are services, not connections.

gmx.com
Also called by 2 other listings
go.mail.com
Also called by 2 other listings, including MailCheck
mail.com
Also called by 2 other listings
gmx.net
Also called by 3 other listings, including Fenerbahçe SK Anasayfa, beşiktaş-jk-anasayfa
go.gmx.com
Also called by 3 other listings, including WEB.DE MailCheck for Firefox
search.gmx.com
Also called by 3 other listings, including WEB.DE MailCheck for Firefox
suche.1und1.de
Also called by 3 other listings, including WEB.DE MailCheck for Firefox
suggestplugin.1und1.de
Also called by 3 other listings, including GMX MailCheck for Firefox
suggestplugin.gmx.com
Also called by 3 other listings, including GMX MailCheck for Firefox
suggestplugin.gmx.net
Also called by 3 other listings
suggestplugin.mail.com
Also called by 3 other listings, including GMX MailCheck for Firefox
suggestplugin.ui-portal.de
Also called by 3 other listings, including WEB.DE MailCheck for Firefox, GMX MailCheck for Firefox
suggestplugin.web.de
Also called by 3 other listings
s.uicdn.com
Also called by 4 other listings, including MailCheck
search.mail.com
Also called by 5 other listings, including MailCheck
suche.web.de
Also called by 5 other listings, including MailCheck
adsensecustomsearchads.com
Also called by 6 other listings, including MailCheck, MailCheck
dl.web.de
Also called by 6 other listings
suche.gmx.net
Also called by 6 other listings
1und1.de
Also called by 7 other listings
bs.navigator.gmx.net
Also called by 7 other listings
bs.navigator.web.de
Also called by 7 other listings
netid.de
Also called by 7 other listings
oauth2.gmx.com
Also called by 7 other listings
oauth2.gmx.net
Also called by 7 other listings
oauth2.mail.com
Also called by 7 other listings
oauth2.web.de
Also called by 7 other listings
wikipedia.de
Also called by 7 other listings
dl.mail.com
Also called by 8 other listings, including MailCheck
img.ui-portal.de
Also called by 8 other listings, including MailCheck
dl.1und1.de
Also called by 9 other listings

AI-generated. Findings may contain errors. Those marked Verified have been manually reviewed.

Publishers can request a review.

What it can do

Permissions this extension asks for, as declared in version 8.0.20. Asking for a permission is not a finding on its own - it is what the extension can do if it chooses to.

  • Read and change your data on mail.com

    https://*.mail.com/*

  • Act on the current tab, but only after you click the extension

    activeTab

  • See the address and title of every tab you have open

    tabs

  • Store data in your browser

    storage

  • See, disable and uninstall your other extensions, including your security ones

    management

  • Show you desktop notifications

    notifications

  • Add items to the right-click menu

    contextMenus

  • Sign you in with your Google account

    identity

  • Run searches with your default search engine

    search

Where it sends data

Destinations our analysis observed mail.com MailCheck contacting. Sending data somewhere is not a finding on its own - an extension that syncs your settings has to talk to its own server - but it is where your data can go, and who else it goes to.

  • oauth2.gmx.com

    mail.com MailCheck sends data to oauth2.gmx.com. 2 other extensions we have analysed send data here.

  • oauth2.gmx.net

    mail.com MailCheck sends data to oauth2.gmx.net. 2 other extensions we have analysed send data here.

  • oauth2.mail.com

    mail.com MailCheck sends data to oauth2.mail.com. 2 other extensions we have analysed send data here.

  • oauth2.web.de

    mail.com MailCheck sends data to oauth2.web.de. 2 other extensions we have analysed send data here.

Updated 30 September 2026amo-410856