Encode headers from email part to utf-8 before extracting filename
Encode headers from email part to utf-8 before extracting filename

This isn't an exact fix, UTF-8 encoded content disposition is supported
by most browsers but isn't standard. The actual standard is specified in
RFC 6266, section 4.3: https://tools.ietf.org/html/rfc6266#section-4.3

Inboxen/Inboxen,Inboxen/Inboxen,Inboxen/Inboxen,Inboxen/Inboxen