The best way to understand this issue is to compare it to Fibber McGee's Closet. You can only put so much stuff into a given space before it won't hold any more stuff and it overflows. When your mail overflows it takes up server space that your web site needs. Eventually what happens is that your server space fills up and takes your web site and your eMail down. You then have no web site and no eMail.
If you use a real eMail program, the trick to keeping this from happening is quite simple!
There is a setting in your eMail program's Options or Preferences that you can enable or disable (depending on the program) that will delete the mail off the server when you download it to your eMail program. Setting this properly is usually just a matter of checkmarking or un-checkmarking a box! When properly enabled, every time you check your eMail, the mail comes into your eMail program and is removed from the server at the same time. Your mail only accumulates on the server until the next time you check your eMail.
In Eudora the setting for this is found by going to Tools --> Options --> Incoming Mail.
Below is a screen shot of the Eudora settings window I get when I access this option. Look for the arrow pointing to the checkbox setting. If I were to checkmark this (enable it) my mail would be left on the server which is what I don't want. By leaving this box blank, my mail does not accumulate on the server. Settings for each eMail program are not necessarily found in the same place in personal preferences or options.
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You will find alternative settings in my screenshot example. Deleting the mail from the server on download is the most effective, especially if you are one to receive an abundance of spam mail and/or not one to check your eMail on a frequent basis.
For you Outlook Express users, you can check out this tutorial. Since I'm not an OE user I cannot say that it follows all versions of Outlook, but I'm going to venture a guess this will help you no matter which version of OE you use.
Web mail is not immune to the issue of accumulating mail. What happens if your mail overflows? Our adminstrative staff does receive notifications of accounts that go over quota. What we have to do then is to upgrade your hosting account to accomodate the overflowing amount of mail. If we don't do this, eventually your web site account (including your eMail) will go down as you will be out of space. If we need to upgrade your account, your hosting fees increase accordingly.
We notify you of over-limit issues, and it's up to you to take care of the problem.
You can and for your own sake, must keep your own eMail in check. The way to handle the accumulation in web mail is different than for those who use a real eMail program.
Take advantage of the built-in Monthly Maintenance feature. Once a month, your web mail will automatically offer you a maintenance option that assists in the cleaning up of old mail and attachments. This feature and it's settings are found in your web mail interface under Options --> Global Options --> Login Tasks. The option to complete the maintenance tasks will pop up around the first of the month when you login to your webmail account. Use it to your advantage!
The Monthly Maintenance feature will not delete mail from your Inbox or your Sent Mail box. These must be handled manually by you.
The fact that the Monthly Mainteance feature will be offered automatically if you enable it is a built in reminder for you to follow up by:
Deleting all eMails from your Inbox, Sent Mail box and any other mailboxes you've created that you don't absolutely have to keep. Deleting the mail really only moves messages you don't want to the Trash. You must then click the Empty Trash link.
Unless you're bombarded with spam, performing this task once a month should keep your unnecessary mail to a minimum. This keeps your server allotment within its parameters and your account will not have to be upgraded which of course costs you more money.
If you do receive large amounts of spam, it's to your advantage to manually delete and empty the trash on a more frequent than monthly basis.