below information is taken from saratogahosting.com
By default your iPhone will never delete messages
from the server unless you have it specified in the
iPhone settings. This presents two possible serious
problems you're likely to encounter:
A) Your inbox quota on the server becomes
full and rejects incoming messages if you
have a reasonable quota limit set on that email
account in your hosting control panel, which you
should. (Recommended server inbox quota is 50-100mb
B) If you have the account set to unlimited
quota in your hosting control panel (not
recommended!) then over time you will fill up your
hosting account server space with massive amounts
of email messages. (Wastes hosting space, reduces
performance, and can cause some major headaches
if you ever get a new device by way of making that
new device have to re-download all of your emails
since the beginning of time with your account!)
NEITHER of those problems are anything that you want
to deal with and so in this article we discuss the
solutions, depending on your preferences.
Note - if you also use a computer to check the same
email account that you're checking with your iPhone,
you'll need to make a small adjustment to the settings
in your email on your computer. We'll provide that
information as well toward the end of this article.
How to fix the problem:
You can make a minor setting change to a particular
email account setup on your iPhone (or iPad) so that
it removes messages from the server every 7 days.
We strongly recommend that you take a moment
to make this setting change:
1. In Settings, select Mail, Contacts, Calendars.
2. Select the account for which you wish to change
3. Select Advanced, located at the bottom of the
4. Select the Delete from server option.
5. Choose Seven Days from the pop-up menu. (*Sidenote*
- We would recommend only 2 or 3 days, but as of
the time of this article the lowest option iPhone
offers is Seven Day)
6. Press the Home button to return to the Home screen.
IMPORTANT NOTE - EVEN THOUGH THAT SETTING HELPS,
IF YOUR iPhone IS SET TO USE "IMAP" INSTEAD
OF "POP3" FOR THE ACCOUNT, THEN IT WILL
STILL LEAVE MESSAGES ON THE SERVER UNTIL YOU ACTUALLY
DELETE THEM / EMPTY TRASH FOLDER ON YOUR iPhone.
So - be sure to delete unnecessary messages
from your iPhone and empty the trash folder regularly.
SECOND PART OF SOLUTION - If you're also accessing
the same email account from a computer then chances
are that the email software on your computer is also
set to leave messages on the server and that needs
to be changed as well.
here to get instructions for setting your computer's
email software to properly remove messages from the