This error occurs because your mailbox has a set limit of space on the mail server. To correct the error you must either remove emails from the server to free up space, or you can request extra mail space. There is a charge for extra mail space.

To clean up your space immediately:
Login to your webmail, and view your inbox and delete items you don't need.
Also clean out the DELETED and JUNK folders if you have them since these are using your space also.

To manage your mail space better:
We suggest that you change your mailbox settings to 'PURGE email when deleted' instead of 'Put deleted email in DELETED folder'.  This is a drop down box setting on your email user settings and the wording varies a little in different versions of SmarterMail, but in general you should 'PURGE' email when deleted so you don't have to delete it 2 times.

Also, if you use a mail client such as Outlook, you can set the mail client to delete emails from the server after it downloads email to your machine. Doing this will automatically remove emails from the server after you download them, so you won't need to login to webmail to do it. A slightly different option in your mail client is that you can have your mail client delete the emails X days after you download them to your client. This is an excellent option for people that download their mail to Outlook on multiple machines (home, work, pda).  You'll need to set the # of days to something that leaves mail on the server long enough for you. One to two days is good for most people that choose this option.