I assume that English is not your first language, as I really don't understand the question.

OK, I will try to correct my bad English (sorry) in the question: I am talking about "Filelink for Large Attachments" in the Thunderbird program. Configuring Filelink according to this link: https://support.mozilla.org/en-US/kb/filelink-large-attachments

When I select the menu option: Edit | Preferences | Attachments and click on the Outgoing button, the Thunderbird program show me Ubuntu One as the "service provider", but Ubuntu One will be down on July 2014, then I try to add a new service provider clicking in the add button and Thunderbird show me the window "Set up Filelink" with a drop-down list with only 2 service providers: "Box" and "YouSendIt" but nobody of this service providers works with Linux for Sync. then this is (or are) my question: What can the Ubuntu (Linux) users can do to replace the Ubuntu One ? If Thunderbird and Mozilla is and strong partner of Ubuntu (Linux), why is there not any other service provider, like "DropBox" (for example) in your Drop-down list ?

You can use Dropbox by installing this add-on.

https://addons.mozilla.org/en-US/thunderbird/addon/dropbox-for-filelink

OK I solved the problem installing the add-on for Thunderbird "dropbox for filelink" but i Think, that regardless this solution, Thunderbird will need a default service provider like DropBox in order to replace the Ubuntu One service provider that will be down on July 2014.

I think there is very little we can do on that front. I understand there is another provider going to replace Ubuntu One but seriously it is a third part operator in the business to make money. If they support Linux or not is not something we can dictate.