Can I use Squirrelmail or Nutsmail as my only email client?
You need to upgrade to a much larger hosting plan if you want to continue to store hundreds of MB's of email in a 100MB disk quota limited account.
It isn't necessary or even wise to be collecting important email online on a shared hosting server environment like ours. I strongly recommend that all of your users treat Squirrelmail or Nutsmail as if it were TEMPORARY email storage while you are on the road and then use Outlook or the free Thunderbird email clients when you are in the office - both of those products will then clean the incoming email off our server and free up space so that emails don't bounce when you've reached your disk quota limit. I don't know if you are aware of this but you must be bouncing emails from clients if you are over your disk space limit.
You can't continue to ignore these real issues - they are hurting your business and reputation by not addressing them.
You have to move to a desktop based email client and only use web based mail as temporary email when away from the office.
I had a client crying the blues the other day because she was entering into a lawsuit and needed the old emails she had in Webmail . They were gone because she was always over her quota and never paid attention to my pleas to change her email habits. Now - she is going to pay in a big way I suppose. Our Terms of Service and Disclaimers very clearly indicate that we will not be held responsible for any loss of email using our services or third party software.
She is quite upset with us and I understand that but it won't make up for her lax attitude about these real issues that she consciously chose to ignore in the past.
Please take appropriate action to protect yourself.
1) upgrade to a much large hosting plan with much larger space so that you don't risk bouncing emails
2) better yet - switch to Outlook or Thunderbird for all desktops and only use squirrelmail or nutsmail while you are on the road and set the desktop client to clean emails off of the server each time to start up Outlook or Thunderbird.