Attachment is not attached to e-mails

I like Contact Form 7 and everything works fine, but the email attachment is not attached in either the mail to me nor the one to the sender, although the message appears that “sending worked”.

Yes, I put the file in the “E-mail” tab in both mails with the e-mail tag [file-687] given above in the “File attachments” field and also into the both File Attachment fields below.

I tried different attachment sizes – even small ones about 100 KB. None is being attached.
There is also a folder wpcf7_uploads on the server – I gave it public write permission (766).
I have also tried it with a second file and have it displayed in both mails as well (this works – the file name is displayed) and also added both mail tags [file-687][file-173] in the File Attachments field. Nevertheless the e-mails have no attachment.

Thank you very much for any tips that help here!