Why webmail cannot attach files?
Well, some webmail services cannot attach files because they want you to pay for more space on their servers. So, after a while when your email account is full of messages and attachments they prompt you to upgrade your membership or delete mails from your mailbox.
Another reason may be that the file size limit has been reached. For example, for Gmail, you can send files up to 25MB in size which is quite enough to attach 100 images!
There are also some other possible reasons like your browser does not support HTML5 or the recommended plugins are not installed. Try installing Adobe Flash Player, if this still doesn’t work… the web-mail service is not able to attach files for this reason.
Well, it is always better to check with the support service of your webmail or online storage service before you start uploading and attaching files.