I have two Accounts one private one business

my business email outgoing server is mail.xxx
when I close mozilla and open it again it changes to mai.xxxx I cant edit it I have to delete and reinstall the account.
Any Ideas what is going on and how to fix it.

Have you tried:

In Mozilla mail > Edit > Mail & News accounts and set the account as default.

To add a server click on 'Outgoing Server (SMTP)' then 'Advanced' then on 'Add' and add a new server.

To apply a server to a specific account click on the account then click on the 'Advanced' Tab and apply the server you wish that account to use as its server.

***Actually I just re-read your post and I think you may be refering to the 'pop' mail server, if so, sorry I don't know how to change that one. In the past when I have set it up wrong I have done the same way as you by delting the account and starting again.