Cant change mail server settings

Cant change mail server settings

Hi,

We are currently changing over to Zoho mail from using Thunderbird and other desktop clients for our email.
All is going OK and we can receive email into the accounts - however send out emails is not possible.

We have tried to change the mail settings under:
Common Settings>Mail Accounts

However when we change any of these details the do not save and so we are unable to send mail.

Do I have to log in as another user or something?
I am on a mac running OSx and the browser is Firefox 3.
As I say - I can get mail in and read it etc but not send out.

Any help would be good.

Bob