Cheap business email

prowla

You can register a domain with a provider such as freeola/getdotted for not very much, eg. "textbook.co.uk"; you may have a job to find a name which isn't already taken.
You can then create an email address, eg. "theboss@textbook.co.uk" and set your email client to receive and send emails using that address.

didibibim

You can use yandex mail but - trust can be disscussed as long term...