Thunderbird Filelink and Privacy Policy

Mark Banner mbanner at
Wed May 30 15:25:30 UTC 2012

The Thunderbird project has built a feature to make it easier for users 
to send large files to their correspondents. The feature has been 
discussed as part of the normal Thunderbird project management process 
for over a year. The feature page is at:

(although the most punchy motivation is best explained by XKCD:

Thunderbird detects when users are about to send large attachments, and 
lets users opt-in to the feature (called Filelink).  If the user opts 
in, Thunderbird makes it easy for the user to create or connect to a 
storage service like YouSendIt, and then upload attachments to those 
services, if they wish. The links to those attachments are then 
automatically embedded into the email.All of the service providers have 
free plans.

This thread is specifically to inform a broader set of community 
members.  We believe the feature aligns with our Privacy Principles 
matches user expectations, and moves the Mozilla Mission forward.

You can try the feature out with Thunderbird Beta builds, available at:

It is important to note that attachments are not stored on Mozilla 
servers, and the partners service come with their own privacy policies, 
terms of service, and that the feature has already gone through privacy, 
security, and policy reviews.


Q: Does Mozilla have any server-side data about which users have picked 
what provider?
A: No.

Q: What storage services are currently supported?
A: Right now, we're supporting YouSendIt. The UbuntuOneand 
SpiderOakstorage services are planned to be addedin future releases.

Q: What about encryption? Can these storage services view my attachments?
A: Unless you've encrypted the file before uploading, the storage 
services will be able to access the file you've uploaded - as will 
anybody who obtains the link to the attachment.  Users should decide on 
their own which service provider they trust with that responsibility. It 
should be noted that attachments sent using "normal" means are typically 
legible by anyone in the SMTP chain, and uploads to the service provider 
happenseparatelyover HTTPS.

Q: Can you support service provider X or protocol Y?
A: We've got plans for supporting SpiderOak and UbuntuOne in the future. 
We also have an Up-for-grabs project 
<>available if anybody would 
like to try adding support for more services or protocols. Developer 
documentation for the Filelink feature can be found here:

Q: What happened to supporting Dropbox?
A: We'd love to support Dropbox, but have not been able to reach 
agreement with them yet.  It should be clear that free attachment 
hosting costs service providers money, so each provider needs to opt-in 
as well to being built-in to Thunderbird.

Q: I don't like the idea of storing my files with third-parties like 
this... do regular attachments still work?
A: Regular email attachments still work the same as they always have. 
We've just given you the ability to choose to upload large attachments 
somewhere, if you wish. Thunderbird's notion of what a large file is 
defaults to 1MB, but can be customized in the Attachment pane of the 
Preferences dialog. The offer to upload can also be disabled entirely.
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