Many email servers do not accept messages with large file attachments. The file size restriction varies depending on the mail server configuration. While you might be able to send a message with a large attachment, the receiving mail server might refuse to accept a message with a large attachment. This is all beyond the control of Thunderbird.

Thunderbird’s Filelink feature eliminates this problem by providing support for online storage services. It allows you to upload attachments to an online storage service and then replaces the attachment in the message with a link. The message recipient clicks the link to download the attachment. As additional benefits, sending and receiving large files is much faster and both you and the recipient will save disk space.

Note that you can use Thunderbird Filelink in addition to regular attachments. For example, you can attach small files directly to a message and use Filelink for large attachments in the same message.

The instructions below show how to use Filelink with the WeTransfer online storage provider, which conveniently ships with Thunderbird as we have an agreement with them to integrate their services. The Thunderbird community has also made available a number of Filelink add-ons for other providers.

Adding Filelink

If you want to start using the Filelink feature, Thunderbird’s integrated Filelink provider WeTransfer will be the most convenient option. It just takes a single click to enable WeTransfer once in your Thunderbird OptionsPreferences. For some online storage service providers, you may have to first create a new account or configure an existing account with them.

1. In the menu bar, click the Thunderbird menu and select Settings.Click the menu button and choose Settings.
2. From the navigation pane on the left, select Composition, then find the subsection Attachments. Alternatively, use the Find in OptionsPreferences searchbox at the top and search for: WeTransfer.
3. Click the Add WeTransfer button to enable WeTransfer for Filelinks. Done!
4. Alternatively, follow the Find more providers link for a choice of addons to add other Filelink service providers (more details below).

 [✓] Offer to share for files larger than [ 5] MB

Using Filelink

When you attach a file to a message, and the file size exceeds the size you have specified above, Thunderbird will automatically offer to use Filelink:

• Click the Link button to upload the file to the online storage service provider.
• If you prefer to attach the file as a regular attachment, choose Ignore.

After choosing Link, your file will be uploaded in the background and the displayed message will update to:

When the linking is complete – that is, your attachment has been uploaded to the service provider – Thunderbird will automatically add a section in the message with a link to the online copy of your file as shown below:

When your recipients receive the message, they will see the same information and clicking the link in the message will take them to a page where they can download the attachment.

Filelink FAQ

Attachments that you send via Filelink are not stored on Mozilla servers. Each file storage service provider has its own privacy policy and terms of service. The file storage service provider has reviewed the Filelink feature to ensure that it is consistent with their policies.

Q: Does Mozilla know which provider the user has picked?

A: No. Mozilla is unaware of which provider has been selected by a user. Provider configuration is stored on the local machine.

Q: What storage services are currently supported?

A:

• We have an agreement with WeTransfer to integrate their services directly into Thunderbird, which is the most convenient option.
• You can install support for more third-party providers with Filelink add-ons. A number of popular providers are supported.
• You can also use Filelink with your preferred WebDAV server with the Filelink provider for WebDAV add-on.

Q: Can the storage service view my attachments?

A: Unless you encrypt the file before uploading, the storage services will be able to view the file, as will anyone who obtains the link to the attachment. Users must decide on their own which service provider they trust with that responsibility. Service providers will generally explain your privacy rights in their terms of service. Note that standard attachment functionality is also not encrypted. When you send an attachment the "normal" way without using Thunderbird’s OpenPGP or SMIME features, the file can be accessed by anyone that can access the message between your system and the recipients system (such as your email service provider). Filelink adds some security as file uploads to the storage service provider are sent via HTTPS, a secure protocol. We recommend using Thunderbirds OpenPGP or SMIME features for maximum security of your communications.

Q: How long will my file be available on the storage service provider's site?

A: For the free service of WeTransfer, the file which you uploaded via Filelink will be available for download for 7 days. If that’s too short, you can sign up to their paid service. Depending on the terms and conditions of your third-party storage service provider and your service agreement with them, the file may remain available on the provider’s site for a limited period or until you explicitly delete it. You will need to log in to the provider’s website to view and delete the files in your personal storage space.

Q: Can you support service provider X or protocol Y?

A: Please check if the Thunderbird community has provided a Filelink add-on for the service provider you are looking for. Developer documentation for the Filelink API is available.

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 are just offering you an option to upload large attachments somewhere else if you wish. Thunderbird's notion of a large file defaults to 5 MB, but can be customized in Thunderbird’s Preferences:

1. In the menu bar, click the Thunderbird menu and select Settings.Click the menu button and choose Settings.
2. From the navigation pane on the left, select Composition, then find the subsection Attachments. Alternatively, use the Find in OptionsPreferences searchbox at the top and search for: WeTransfer.
3. [✓] Offer to share for files larger than [ 5] MB

Removing the checkmark will prevent the automatical Filelink notification when you attach big files, but the Filelink feature will still be available from the Attach | v button dropdown as well as other attachment menus and context menus.