How to Find Mailbox Capacity
Most email systems designate a certain amount of room for an email address. Every email, picture, video and attachment has to be stored on a server. If you are using an online email account, you can usually search in the menu settings to find out what kind of limit you have (online email accounts save everything to an online server). Other desktop based programs such as Outlook store the information on your main computer.
Open Outlook and press "CTRL+6" to see the folder list.
Select "Folder Sizes." The used capacity will be listed in the "Folder Size" box under "Total size."
Subtract the amount listed under "Total Size" from the total capacity. Home users will have a total capacity of 2GB, while those on a server might have a different amount. If on a network server you will need to contact your administrator to ask what limit has been set for you.
Log into your Gmail account and scroll to the bottom of the screen. The capacity will be visible and will look something like "You are currently using XXX MB of XXX MB."
Log into your MobileMe email account. Click the "Account button" from the toolbar, then click on "Storage Settings." You can view your mailbox capacity under the "Personal Storage" section. Apple MobileMe generally has 20GB of storage for a full account and 5GB per Family Pack child account, though this amount can be modified by the account user.
Check the homepage of your online email account for updates on storage size. Several popular online email websites offer unlimited capacity such as Yahoo and AOL. Hotmail offers 5GB to start off with and adds more storage space every day to make sure you can never run out of room. The capacity changes regularly, so check for updates.