Sometimes certain inbound or outbound message is tagged as spam because the message attachment did not meet RFC2183 standards.
RFC2183 is an attachment filtering option in mymailsecurity. If a message is tagged with the error message that you’ve provided in your quarantine, this means that the message sent to or from you does not meet this RFC2183 standard.
You can disable this this option from the Attachment Filtering page for the either the whole enterprise or for individual users.
Messages that do not meet RFC2183 standards generally have attachments that do not have correctly formatted file names or extensions. This is common in read receipts, calendar invites, and messages forwarded as attachments.
RFC2183 non-compliant messages can be used to launch attacks against mail servers.
Applies to the following Optimus Systems products
mymailsecurity Email Security