To help us make sense of your question, please tell us which 'Outlook' it is that you're referring to.
For many, many years, the standard email 'client' (= program) on office computers (and many home computers too) has been Microsoft Outlook. It can be used to send and receive email from any account (such as ones ending @btinternet.com, @yahoo.co.uk, @somefirm.co.uk, etc).
However, Microsoft then totally confused things by rebranding their web-based email service from 'Hotmail' to 'Outlook', even though it's got absolutely nothing to do with their email client of the same name (and only refers to email addresses ending in @outlook.com or the older @hotmail.com).
So, when you refer to 'Outlook', do you mean a program which you use on your computer specifically to send and receive emails or the Outlook.com website (which you access via your web browser).
I'm sorry to have to trouble you with my question but experience has shown that posts about 'Outlook' often end up with loads of answers that will make no sense to the questioner at all because they're referring to the wrong 'Outlook'!