Difficulty setting up additional emails

Hi I am trying to set up additional accounts and error message says '''''incoming server already exists.'''''... but it doesn't. It's accepted my gmail emails ok, but trying to add my business domain emails. Initially had difficulties with the right settings (given incorrect info from my Server host) then when I finally get all the boxes ticked, it comes up with the error message... but I have looked through the settings and only the gmail addresses are in there, How do I get around that please? Thank you for some assistance... Thunderbird was suggested to use in lieu of outlook, by my domain hosts... yet they've bolted with a care factor of zero and not solving any of the issues today... Cheers, Jay D