Reply To: Attachment Link in Mails are broken

now i can finally produce the error. It seems to be due to the size and number of attached files. If I attach more than 2 images with 9,5MB file size each I get an ajax error. See attached file (screenshot). And then you can still click out of “Send” and the mail is delivered without images.

The customer really wants to allow 10MB images and get at least 5-7 images attached.

What can I do?