There are many reasons for the cannot attach files in yahoo mail issue. The type of attachments with names made up of special characters are not accepted by email. For instance, the message won't connect your attachment if its name contains hashtags, dollar signs, or slashes. If you see that your file name contains symbols other than letters, such as punctuation marks, remove them. Yahoo, on the other hand, allows messages to be up to 25 MB in size overall. This means that your file cannot be that big.
