Automatically Reduce Images Before Sending In Thunderbird

Martin Brinkmann
Mar 6, 2012
Updated • Jun 26, 2017
Email, Thunderbird

Photos these days come often in the Megabyte range which makes it difficult to transfer them via email or other means.

Email is special as it is usually limited in regards to size which you will notice once you try to send an email with a 60 Megabyte attachment as it will bounce and not reach the recipient.

The limit is usually in the 15 to 25 Megabyte range, with companies like Microsoft working their way around the limit by hosting the attachments in the cloud, and replacing attachments with links to the cloud hosted files instead.

Some users help themselves by running their photos through image optimizers like Riot, VSO Image Resizer, or a dozen of other image resizers that optimize photos and images so that they take up less space.

Shrunked Image Resizer

shrunked image resizer

The Thunderbird extension Shrunked Image Resizer handles the task automatically whenever you send images as attachments.

The extension displays a configuration dialog whenever you do, that allows you to select a desired maximum resolution for each photo as well as the quality of the converted images.

You can furthermore define a minimum file size in the extension options. All images below that size are not converted at all, while all greater than the selected size are.

Once you have made your selection you will see a progress bar coming up when you send emails that indicates the conversion progress. The process itself should not take long, and you will notice that large images are reduced significantly in size by it.

resizing images

Note that you may still run into maximum attachment size issues. It depends entirely on how many images you have added to the email, and the resizing operation.

There is no preview of the output image which is one of the things that could be improved by the author as here is no way currently to check the quality of the converted images.

You could send the first batch of images to your own address to verify the quality of the conversion before sending them to other recipients.


Shrunked Image Resizer regardless of that is a useful extension for Thunderbird users who often encounter issues when sending photos as attachments in the email client.

The extension has its shortcomings, namely that there is no preview and that there is no indication in regards to the size of all attachments after they have been processed.

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  1. zimbo said on January 7, 2022 at 6:42 pm

    thanks for this addon, using it a long time yet.

    Is there a chance to get the functionality to shrink images in incoming mails too? Would be great to have this!

  2. Rick said on March 6, 2012 at 7:11 pm

    My favourite is still Shrink Pic (; it reduces all image files that are being sent from your pc, not just email. An oldie but a goodie.

    1. Rick said on March 6, 2012 at 7:16 pm

      PS Martin – your RSS feed isn’t working through Google right now. Working via Thunderbird but not my normal igoogle feed link.

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