New Account @mail.uk only shows in-box

I am trying to replace my Outlook account which has been blocked by Microsoft AI and remains blocked after multiple attempts to get it working again. I have just added a new account and can send @mail.uk e-mail from Thunderbird. However, there is only an in-box folder shown on Thunderbird and no trace of the sent e-mail - although I can confirm that is was received by two test recipients. I did consider a Thunderbird e-mail account as a replacement but, at 79, I avoid additional costs whenever possible. Can you suggest an alternative free e-mail service which works on Thunderbird? My g-mail account used to work but now I am having password problems.