How to connect owncloud to Roundcube?

Question

Roundcube

There is such a web muzzle for mail - Roundcube. And everything in it is good, but I want it to be like on mail.ru - when uploading large files, they should be uploaded to the cloud, and a link should be sent. Actually there is also a cloud - Owncloud.
By default, Roundcube downloads all attachments at once and inserts them into the email, so it cannot download more than the mail server will allow, or more than the maximum POST request in php.ini. But how to make it send the file to Owncloud and take the link?