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I am an emeritus professor using the UVM email account X@uvm.edu<mailto:X@uvm.edu>, which I have used for many years. I use Mozilla Thunderbird (current version, “Eclipse”) as my email client and my account is configured for UVM’s Microsoft 365/Exchange Online service. After my most recent required yearly password change, although I can still receive email in Thunderbird, I can no longer send email. When I attempt to send a message, I consistently see this error: “Login to account ‘smtp.office365.com’ failed. Login to server smtp.office365.com with username tosler@uvm.edu<mailto:X@uvm.edu> failed.” Here are my current settings: * Incoming (IMAP): * Server: outlook.office365.com * Port: 993 * Connection security: SSL/TLS * Authentication method: OAuth2 * Username: tosler@uvm.edu * Outgoing (SMTP): * Server: smtp.office365.com (I have also tested smtp.uvm.edu with the same result) * Port: 587 * Connection security: STARTTLS * Authentication method: OAuth2 * Username: X@uvm.edu I have reinstalled Thunderbird, and I have removed all saved passwords and tokens for outlook.office365.com and smtp.office365.com, restarted the program, and completed the Microsoft/UVM sign‑in prompt again. IMAP continues to work and mail arrives normally, but SMTP authentication still fails with the error above. Because: * The configuration matches Microsoft 365/Exchange Online client‑submission settings, and * IMAP with OAuth2 works, while SMTP with OAuth2 fails, it appears that this may be a server‑side policy or mailbox setting, rather than a client configuration problem. What are my options? Does the University of Vermont have to change some setting on their end on my behalf? Thanks. -turner (PII redacted by moderator)