''<p>Linnéa [[#question-1450587|said]]</p>'' <blockquote>Hi I cant find an Add-On for blocking ads in newsletters. </blockquote> That is because there is not one. <blockquote> How can I block the very annoying Ads in newsletters? These newsletters from mainstream newspapers are a real imposition. </blockquote> Most folk just block the remote content in the emails. <blockquote> How-To block ads in mails with Thunderbird? </blockquote> You could try not subscribing to email that contain the annoying advertisements. If everyone withdraws their support, eventually those that insist on advertising will wither and die, but they might try offering a paid service first without advertising.

uBlock Origin works with Thunderbird here. https://addons.thunderbird.net/en-US/thunderbird/addon/ublock-origin/ Note, you'll have to open messages in tabs though.