Beginning a few days ago we increased the maximum quotas for paid mailbox upgrades. The maximum available had been 400MB for a long time, and we've increased that to 3.1GB (3100MB). The default quota for all mailboxes is still 100MB, which is all you need if you mostly use POP and store your email on your computer. If you mostly use Web Mail or you like to leave all your email on the server, then you might need a higher storage quota.
Get more information from this FAQ:
To purchase email upgrades log into your MyAcccount at myaccount.earthlink.net. Complete instructions are at the link above.