Error adding attachment with non-english characters sent via email

When users send emails with attachments containing Norwegian characters (æ ø å / Æ Ø Å) to our Service Desk they are not added to the issue.

Instead we receive the following error.

Adding an attachment with theese letters using drag & drop or browsing directly in JIRA works, so im suspecting the mail handler to be the issue.

webwork.i18n.encoding is set to UTF-8.