'''1. '''Firewall: your Firewall may be controlled by your Operating System eg: Windows OS has Defender. If you have installed an Anti-Virus program then it might be controlling the Firewall. You need to make sure Thunderbird is not being blocked by the Firewall. Do not switch it off because they default might take over and you do not want to operate without a firewall. Just set up to allow Thunderbird. * Exit Thunderbird * Access Firewall * Set up the Thunderbird program thunderbird exe file as allowed and do the same for the updater exe file. Please check your Firewall has this all set up and then tell us this has been done. '''2:''' If you have VPN - switch it off '''3.''' If you create/maintain a website you might use software that uses the 'localhost' - eg: Apache Xampp SWitch it off until you have account up and running. You may be aware that recently Microsoft changed the Authentication Method when it comes to using third party email clients eg: Thunderbird. However, they have also altered what password to use and what email address can use the SMTP. Read on: '''4'''. Your microsoft account and your hotmail/outlook/msn/live account and any other account using outlook server all need to have the same password. So all your microsoft accounts need to be using same password. Info at this link says: * https://support.microsoft.com/en-gb/office/how-to-sign-in-to-hotmail-c378938b-c0eb-40c1-b99e-338dd9e776a8 '' Can't sign in to Hotmail or Outlook.com?'' ''Notes: Your Hotmail or Outlook.com password is the same as your Microsoft Account password.'' You must logon to the webmail account via browser to sort it out. Once all your accounts are using same password..... '''5.''' In microsoft account accessed via a browser If you have more email addresses or hotmail addresses etc , microsoft now regard one is 'primary' and all others are alias to the account. This is not a problem when it comes to receiving mail, but can be an issues when you want to send. When it comes to 'sending' - that is smtp in Thunderbird - it can only send using the 'primary' email address. You can choose what you want to be set as 'primary', but whatever email address you set up as 'primary' - only that email address can be used for SMTP in all imap accounts. So if you want to send using hotmail email address then make sure it is set up as the primary email address. But then if you have an outlook.com account as well, it will only be able to send using the hotmail primary email address. So choose the email address which you want to set up as 'primary'. '''6''. In Thunderbird, Cookies must be enabled in order to set up Oauth. * Settings > Privacy & Security * Check under Web Content - * Select: 'Accept cookies from sites' * Accept third party cookies' 'Always' * Click on 'Exceptions' button next to Accept cookies from sites to make sure you are not blocking cookies from Microsoft sites, such as :hotmail.com, outlook.com, office365.com, www.live.com, www.msn.com '''7.''' In Thunderbird....When creating account or if account is created but you need to check server settings: Account Settings must use the following: Server Type: '''POP''' Mail Server * Server Name: outlook.office365.com * Port 995 * User Name: xxxx@hotmail.com * Connection Security: SSL/LTS * Authentication Method: OAuth2 Server Type: '''IMAP''' Mail Server * Server Name: outlook.office365.com * Port 993 * User Name: xxxx@hotmail.com * Connection Security: SSL/LTS * Authentication Method: OAuth2 '''SMTP:''' * Server Name: smtp.office365.com * Port: 587 * Connection Security: STARTTLS * Authentication method: OAuth2 * User Name: example@hotmail.com (Please note this must be whatever email address is set up as the 'primary' email address) Once you have all these settings and got the password sorted. Restart Thunderbird When you get the Microsoft pop up window asking for password, type it in and click on 'Sign in'. You may then get another window asking to allow Thunderbird access to server - click on 'Accept' Other things to check if still an issue: * In Thunderbird * Via Menu Bar: Tools > Developer Tools > Error Console * Empty the Error Console - use the bin icon top left * Close Error Console * Restart Thunderbird * Try to Get Messages and also try to send an email * Open Error Console If you see anything like this: ''mailnews.smtp: Command failed: 535 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant. Visit https://aka.ms/smtp_auth_disabled for more information.'' That link goes to this location - I specifically include the info on 'enable smtp': https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission#enable-smtp-auth-for-specific-mailboxes It means user is not enabled for SMTP. After switching smtp on - all should then send ok. Do you see 'disabled for the Tenant' error message? Maybe IMAP is also not enabled ? OR does Error Console show something like this - Unrecognized command 'Length: 7' ? eg: ''mailnews.smtp: Command failed: 535 Authentication unsuccessful [MN2PR05CA0041.namprd05.prod.outlook.com 2024-09-25T20:33:37.105Z 08DCDD14E4ECBF59]; currentAction=_actionAUTH_XOAUTH2 SmtpClient.sys.mjs:602:19'' ''mailnews.smtp: Command failed: 500 Unrecognized command 'Length: 7' [MN2PR05CA0041.namprd05.prod.outlook.com 2024-09-25T20:33:42.231Z 08DCDD14E4ECBF59]; currentAction=_actionAUTHComplete SmtpClient.sys.mjs:602:19'' That implies you are trying to send using an alias email address which has not been set up as a 'primary' in the microsoft account or you have not set up all accounts to use same password. It might be useful to post info on what you see in the Error Console.