[Thunderbird] Send attachments as real attachments

There is an implicit setting in Thunderbird. It will treat the attachment with "inline" in the attribute of "Content-Disposition", which will trigger the attachment be showed in mail body when viewing.

There is a way to turn it off.

In Thunderbird,
Tools -> Options -> Advanced -> General -> Config Editor

Set the value of "mail.content_disposition_type" to 1

Now, it works.

BTW, I read Aaron Toponce's article to get this useful solution and you can find the article here.