IMAPSize is a portable freeware Windows application that allows you to quickly and efficiently manage your IMAP mail accounts. It is not another mail client. The main purpose of IMAPSize is to locate space consuming folders and allow you to manage them, hence putting your storage quota under control. To accomplish this task IMAPSize offers a variety of useful (and some unique) operations. Features

• Display of all mailboxes in an account with visual alerts for the most space consuming mailboxes
• Convenient storage quota display
• Powerful search capabilities on single or multiple mailboxes
• Delete attachments (all or individual) without downloading them
• Save attachments locally from multiple messages (BETA)
• Mailbox management (expunge, create, delete, rename)
• Message management (change flags, copy, move, delete, etc)
• Manage folder subscriptions
• Modify message headers
• Copy messages from one IMAP account to another
• Perform incremental backups of multiple folders in your IMAP account
• Perform incremental backups of the whole account
• Replicate IMAP folder hierarchy to your local drive
• Download/upload messages to/from mbox and eml files
• eml2mbox conversion
• mbox2eml conversion. This can be extremely useful in the process of moving messages from Thunderbird to Outlook. Here's how.
• Spam handles which provide a basis for visual alerts on spam messages
• SSL connections
• Minimizes bandwidth consumption wherever possible
• Keyboard friendly - you can perform almost all operations without using the mouse.