Content-Disposition for email body

Question

As far as I understand Content-Disposition header can by userd for any body part of email message

It specifies the "Content-Disposition" header field, which is optional and valid for any MIME entity ("message" or "body part")

RFC 2183

I saw that many mail clients set Content-Disposition header only for attachmetns body parts.

The question is: is it normal to set Content-Disposition to inline for message body (text/html/email body) ?

Answer 1

What do you mean by "normal"?

It's acceptable to set Content-Disposition to "inline" for the message body, but as you noted most mailers only use Content-Disposition to set it to "attachment". And setting it to "inline" generally doesn't make any difference to how a mailer is going to display the message. That is, you can't force it to display some content inline if it doesn't know how to, or if only considers additional body parts as attachments.