Check File Format and Size
Before troubleshooting further, it’s important to ensure that the attachments you’re trying to open are in a supported file format and within the permissible size limit. Yahoo Mail supports a wide range of file formats, including documents, images, videos, and compressed files. Additionally, there is a size limit for attachments, usually around 25MB. If your attachments exceed this limit or are in an unsupported format, Yahoo Mail won’t be able to open them.