530 5.7.57: Client not authenticated to send mail

Microsoft 365SMTPSign-in problem

The error usually looks like this:

530 5.7.57 Client not authenticated to send mail. Error: 530 5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM

What it means

Your app tried to send an email through smtp.office365.com without signing in first.

Common causes

  • Authentication (SMTP AUTH) is turned off in your app, printer or scanner settings.
  • The app tried to sign in, failed, and then tried to send anyway.
  • The app is not using STARTTLS on port 587, so it never got as far as signing in.

How to fix it

  1. Turn on SMTP authentication in your app and enter the full email address as the username.
  2. Use smtp.office365.com, port 587, with STARTTLS.
  3. Run your app against our SMTP connection tester to see exactly what it sends.

Tools to help diagnose it

SMTP connection tester

Spin up a real SMTP test server and diagnose your email sending configuration in real time

Email server checker

Check any IMAP, POP or SMTP server’s encryption, certificate and supported sign-in methods

Email server settings finder

Find the IMAP, POP, and SMTP server names, ports and encryption settings for any email address

Can’t update your app to use OAuth?

Auth-Email fixes sign-in errors like this one without changing your app, printer, scanner or script. It signs in to Microsoft 365 with OAuth on your app’s behalf, while your app keeps using a normal username and password over IMAP, POP or SMTP.

Read the docsTry Auth-Email →

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