Mail.app: Moving Emails from local folder to imap folder -> HDD space decreases temorarily At the moment I am moving large quantities of Emails from a local folder in Apple's Mail.app to an imap folder. I am talking 10+ GB here and more than 10,000 Emails. I am using Mac OS X 10.6.8. It is a slow process, which is to be expected. It happens what is supposed to happen: Emails vanish in local folder and appear in imap folder.

What happens that I do not get is that HDD space decreases considerably during the process (approximately the same amount of GB I move) and stay down temporarily but for a considerable amount of time (several hours). Theoretically I am supposed to have around 9 GB of free space on my hard disk which went down all the way to zero and has in several hours recovered only to 2.5 GB again and goes up only very very slowly.

My guess is that this is what is suppose to happen in the process, but I would be interested in what exactly is happening here. Why does it take up such large amounts of space to move emails and why does it take so long afterwards until HDD space becomes available again?

Thanks.

Edit: Looks like I was mistaken. Space is not recovering. With "Get account info" I see that I moved 8.6 GB to the IMAP Mailbox. At the same time I deleted about 2 GB of files on my system to free up space. With the initial 9 GB I had free on my system I should be at 11 GB. So in fact I actually lose the same amount of space on my system like the emails I moved, since I am now down to about 2GB. But the mails in the local folder are deleted, so normally the space should have been freed up! This does not make any kind of sense to me!
My hypothesis is that what you observe is happening because you are setting your IMAP account not to have all the message for offline consumption, but only headers. If you had it set to full messages, you would be decreasing your space even more, because the IMAP metadata needs to be kept in a database, apart from the full messages.