By linking your Yahoo! Mail account to a Dropbox account, you can share files larger than 25 MB or share files you already have in your Dropbox using Yahoo! Mail and Dropbox integration.

When you try to attach files larger than 25MB, you are automatically prompted to sign-up for a Dropbox account, and link it to your Yahoo! Mail account. By linking your accounts, you can skip the Dropbox sign-in step in the future.

To link your Yahoo! Mail account to Dropbox:

1. While composing an email click the down arrow next to the paperclip icon and select Share from Dropbox.
   -A pop-up menu appears.
2. Click OK. You’re prompted to sign up for Dropbox or to sign in to an existing Dropbox account.
   • If you don’t have a Dropbox account, create a password for your Dropbox account and click Sign Up. Your name and email address are pre-filled in the sign-up screen.
   • If you already have a Dropbox account, click Sign into Dropbox, and enter your Dropbox credentials.
3. On the next screen, click Link account.
   • If you have files in your Dropbox already, you may attach them by selecting each file and clicking Choose.
   • If you began the link accounts flow by attaching a file larger than 25MB, your file will automatically begin uploading to Dropbox.

Sending a file that’s larger than 25MB, after you’ve linked accounts

Sending a file that’s on your computer:

1. While composing an email, drag and drop a file you want to attach from your computer into the body of the email.
   -A dialog box prompts you to use your Dropbox account to send the file.  If you have not linked your account, you will be prompted to link your account.
2. Click OK.
3. The file is uploaded to Dropbox, and a link to the file on Dropbox is inserted into your email.

Sending a file that’s in your Dropbox:

1. While composing an email, click the down arrow next to the paperclip icon, and select Share from Dropbox.
2. The Dropbox file picker will open showing you the files in your linked Dropbox account.
3. Select the file you want to share, and click Choose.
4. A link to the file is inserted into your email.

Note: Recipients of your email don’t need a Dropbox account in order to access the file.

Signing out and unlinking your Yahoo! Mail and Dropbox accounts

Signing out and unlinking from Yahoo! Mail:

1. Compose a new Message.
2. Click the down arrow next to the paperclip icon and select Share from Dropbox.
   -The Dropbox file picker window loads.
3. From the Dropbox file picker, click your name in the top right and select Sign out and unlink.

Signing out and unlinking from Dropbox:

1. Sign in to your Dropbox account on the Dropbox website. 
2. In your Dropbox account settings, find the "My Apps" section.
3. Find the Yahoo! Mail application and click the X to remove it.

You might find this article useful:

• Attaching files to an email