POP settings : https://support.microsoft.com/en-ie/office/pop-imap-and-stmp-settings-8361e398-8af4-4e97-b147-6c6c4ac95353?ui=en-US&rs=en-IE&ad=IE POP access is disabled by default. To enable POP access: Enable POP access in Outlook.com If you want to use POP to access your email in Outlook.com, you'll first need to enable POP access. * Select Settings Settings > View all Outlook settings > Mail > Sync email. * Under POP and IMAP, select Yes under Let devices and apps use POP. * Select Save. POP server name: outlook.office365.com POP port: 995 Connection Security: SSL/TLS Authentication Method: Normal Password SMTP server name: smtp.office365.com SMTP port: 587 Connection Security: STARTTLS Authentication Method: Normal Password Discovered this information which is based on Outlook, but it is an email client so likely to apply to Thunderbird as well. But MS website is only likely to tell you about it's own products! Maybe you need two factor authentication setting up. ''Outlook won't accept my password'' ''If Outlook won’t accept your password and you know you’re using the password for your email account, you might have an email account that requires additional security.'' ''Gmail, Yahoo, iCloud, Outlook.com, and AOL accounts all use two-factor authentication to help verify that you’re the person trying to access your email account.'' ''To add your email account to Outlook, you’ll need an app password, also known as an application password. This is a different password than your regular email account password. One way you'll know you need an app password is if you see the following message: 2-factor authentication is set up for your account. Please sign in using your application password.'' ''If you're using two-factor authentication for Outlook.com, use the following steps to generate an app password.'' * Go to https://outlook.com, click your initials in the upper right, and then select View Account. * Under Security, select Update. * Under More security options, select Explore. * Scroll down to the app passwords section, and then choose Create a new app password. * Your app password will be displayed on the next screen. Make a note of this password, as you'll need it when you add your account to Outlook. * When Outlook asks for your password, enter your app password. So where it requires Password in Thunderbird when creating the account, enter the app specfic password. Authentication Method: should still select 'Normal Password'.