Why Can't I Attach Files in Yahoo Mail?

Big Files
Yahoo Mail limits the size of each email. This includes all text, graphics and attachments. Check your file size to see if it exceeds 25MB. If it does, you won't be able to attach it to your Yahoo email. As an alternative, upload it to a file-sharing website and send the link to the file in your email instead of the actual file. If you're sending a photo or PDF file, try lowering the resolution to Web or screen resolution before sending to reduce the file size.
Number of Attachments
You can attach up to 50 files to one email in Yahoo Mail. If you are sending many files in one email and get an error message, count the files already attached. If 50 files are attached, send that email and compose another one in which to attach the remaining files. Yahoo Mail allows you to 'Shift-Click' and choose multiple files, so count before trying to attach, or none of them may attach.
Same File
Yahoo Mail won't let you attach files with the same name in the same email. If you are getting an error message while adding multiple files, review the files to make sure you aren't trying to attach the same file twice or two files with the same name. If you have two drafts in different folders that share a name, rename one of them and then attach it to the email.
Old Version
Ensure are using the most recent version of Yahoo Mail. As older versions are replaced, some of their features may begin to work incorrectly, such as attaching files. Visit the main Yahoo Mail website to upgrade your email account. If you log in to your Yahoo Mail account, check the top of the screen to see if it asks you to 'Upgrade to the Newest Version of Yahoo Mail.' Even if you upgrade your account on your personal computer, your Yahoo Mail may not appear upgraded on a different computer, such as a work computer, if no one has downloaded the newest version on that computer. Download the newest version on each computer you use to send attachments.
Folders
Yahoo Mail allows you to attach files, not folders. If you are trying to attach an entire folder, try opening the folder and selecting the contents. Drag and drop the contents into your email or click 'Open' in the Attachment dialog box to attach them to your email. They will show up as a list of files, not contained in a folder. The email recipient must organize them in a folder on his computer once he receives the files.