A number of e-mail providers use a "URL mangling" service on links in emails, ostensibly to improve security, that redirects all links through a third-party checker service. The two most common such services are the "SafeLinks" service provided by Outlook and the "URLDefense" service provided by Proofpoint.
I don't like it at all, because I think it prevents you from assessing whether the email points to a safe destination or not.
It is unfortunately impossible to deactivate the safelink feature (except for personal accounts I guess?), and this is where this extension comes in play. It replaces all occurrences of Safelinks- and URLdefense-encoded links from emails displayed in Thunderbird, and replaces them by their original value.
Head to https://addons.thunderbird.net/en-GB/thunderbird/addon/safelink-removal/ and install the extension.
In order to build this extension on Linux/MacOSX, execute these lines
# Clone the repository
git clone https://github.com/cphyc/thunderbird_remove_safelinks.git
# Move into the newly-created folder
cd thunderbird_remove_safelinks
# We use node + npm to build the project
npm install # install the required files
npm run build # create the bundled extension, located in web-ext-artifacts/You can then install the extension by loading it directly in Thunderbird using the generated .zip file located in thunderbird_remove_safelinks/web-ext-artifacts/.
Note that if you install this way, you need to manually update the repository, rebuild the extension and reload it in Thunderbird in order to update it.