OK so after talking with Sage they do not have a solution to this as yet, but one needs to be resolved.
I have used Sage for over 35 years and this is the first time I have come across this. I have Sage and am currently using 3 companies, all with different email set ups, i.e., gmail, outlook, etc., so if you go into one company and change it to show the correct email details, then OK etc. then do a test or send yourself an invoice or statement it shows that it is coming from the correct email address.
BUT then you go into the next company, and the email default has changed to show the 1st company email default - so you change that etc, and OK etc., then do another test run, it shows on your emails coming from the correct email address.
Basically at present Sage do not have an answer to this - apparently if you use 2 or more companies on the same Sage set up, although you log in and out, whatever the email default is set to or last used, that is the one it will use.
This isnt any good when you are running two or more companies and sending invoices to customers when it will show the wrong email default address.
They are going to look into this to try and find an answer and Ill keep working out a way forward...