What is your evidence for saying that deleting a message doesn't also delete any attachments?

When you delete a message in Thunderbird it isn't actually deleted. It is marked for deletion and hidden from sight. It won't be removed from the mail store until you compact the folder.

Since an email message is just a series of bytes, there is no concept of header, message or attachment at the file system level. It's just a block of data. That's why I am sceptical of your claim that somehow attachments remain after deleting the message.

Zenos said

What is your evidence for saying that deleting a message doesn't also delete any attachments? When you delete a message in Thunderbird it isn't actually deleted. It is marked for deletion and hidden from sight. It won't be removed from the mail store until you compact the folder. Since an email message is just a series of bytes, there is no concept of header, message or attachment at the file system level. It's just a block of data. That's why I am sceptical of your claim that somehow attachments remain after deleting the message.

I can provide you with pictures, if you ask. I have the same problem too. When I receive emails, I have, let's say 1000mb of data in my inbox (folder size is shown, as you may already have seen). When I delete the unwanted messages with attachments, the size does not alter; if I choose to delete the attachment before email, the attachment becomes unavailable, thus has been wiped out. I understand it is a feature of safety, but at least there should be a function that when I wipe out my trash folder, the attachments are also getting wiped out and the inbox folder size decreased. Nothing such as this happens though.