SMTP block also blocked authentication via POP and IMAP RRS feed

  • Question

  • hello,

    We recently applied authentication policy blocking SMTP in our organization (set-organizationconfig -defaultauthenticationpolicy). For some reason, clients authenticating via POP and IMAP start getting incorrect username/password errors. Only after I allowed them to use SMTP, they start working again.

    I can't wrap my head around it. Does anyone knows why this may happen?

    Thursday, September 12, 2019 4:07 PM


  • Hi,


    It is by design, Authenticated SMTP is used by POP and IMAP client's to send email messages. For POP/IMAP clients, which don't support modern authentication, it needs to allow Basic authentication for the POP/IMAP + Authenticated SMTP protocols and services that they require. Blocking either basic authentication will block app passwords in Exchange Online. For more info, pelase see: Disable Basic authentication in Exchange Online



    Kelvin Deng

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    • Proposed as answer by Alex Riben Friday, September 13, 2019 10:03 AM
    • Marked as answer by cupntea Friday, September 13, 2019 8:22 PM
    Friday, September 13, 2019 5:32 AM