It looks like you've encountered an issue with your email setup in Thunderbird. Since you've mistakenly set up a POP account and then an IMAP account, you're experiencing problems with message downloading and sending. To resolve this, you can start by going to "Tools" > "Account Settings" in Thunderbird. Select the POP account and disable it by unchecking the option to "Check for new messages at startup." For the IMAP account error, make sure you've entered the correct credentials and server settings. Also, double-check your internet connection. If the issue persists, you might need to adjust your Office 365 security settings to allow Thunderbird access. You can find more detailed steps in the Thunderbird support documentation or reach out to Microsoft's support for Office 365.