NOTE This functionality is only available starting in Thunderbird version 8.
You may encounter a situation in which a message you are viewing contains "hidden" attachments, i.e., attachments that are not visible in the displayed attachment list, and you wish to access them as attachments. The two most common circumstances in which this occurs are:
inline images, sound files, etc.
emails which are improperly formatted, i.e., the software on which the email was written put the attachment(s) in the wrong place within the message structure
These hidden attachments can be viewed by switching your message viewing mode to View > Message Body As > All Body Parts. However, because this functionality is not useful to most users and may be confusing to some, it is disabled by default. To enable it, install the "Show All Body Parts" add-on .
Note that your View > Message Body As setting is persistent, i.e., once you change it, it affects not just the message you are currently viewing, but all messages you view, until you change it again. Therefore, you may wish to change it back to one of the other viewing modes when you are finished doing what you need with the attachments.
Another use to which we've heard some users put this viewing mode is removing redundant alternative body parts. The text portion of many email messages nowadays is sent in "multipart/alternative" format that includes both a plain-text and HTML version of the textual content. Some people like to throw away the plain-text or HTML version of the content, especially for large messages, to save space in their mailboxes. When you enable View > Message Body As > All Body Parts, the different parts of the multipart/alternative section of a message will show up in the attachments list as, for example, "Part 1.1.1" and "Part 1.1.2", with icons next to them showing their types, e.g., plain-text, HTML. You can right-click on one of these attachments to delete it from the message, save it, etc. You can also double-click on one of these to open it outside of Thunderbird, just like any other attachment.