Forwarding an email with attached eml multiplies attached files

If you forward an email containing an eml with attachments (such as a PEC with attachments), the mail to the recipient arrives with the attachments multiplied.
In practice, the files are extracted from the attached email in eml format and are forwarded together with those that remain included in the original email.

Steps to reproduce

• starting from a certified email with at least one file attached
• forward the email to an internal user (not PEC)
• open the e-mail from the recipient user (alternatively open the e-mail copied in the sent mail folder)

Expected behaviour

• the email shows the single attachment file as it was in the original email

Actual behaviour

• the email shows the duplicate attached file (the files linked to the PEC are also duplicated (eg: daticert.xml)

Thanks to Marzio Bordin (Ref: #127406)