Office 365 Accounts Suddenly Stop Working


If you were using an Office 365 Account in Postbox successfully but now suddenly find that it is no longer working when you haven't changed any settings in Postbox, then there could be a server change that is causing the problem.

Here's how to get back up and running:

1) Ensure that your server is set up to support POP/IMAP or SMTP

Please don't assume POP/IMAP or SMTP is enabled. If your account stopped working, this could have been the change that disabled assess within Postbox. To check for this:

  • Log into your Microsoft email account using a web browser
  • Click the "Gear" toolbar icon in the upper right corner, then click the "View all Outlook settings" link at the bottom 
  • Click Mail > Sync email

If you see the Sync email link, then either IMAP or POP has been enabled, but unfortunately, this screen doesn't tell you which service has been enabled or if both have been enabled. As such, it's possible for you to see, for example, IMAP settings when IMAP isn't actually turned on.

If you do not see the Sync email link, then IMAP and POP have yet to be enabled, and they either need to be enabled by you (if you're the account admin) or your IT administrator.

Important: Authenticated SMTP must be enabled. If you can receive messages but not send them, please get in touch with your IT Manager or ISP and submit a request to enable Authenticated SMTP.

GoDaddy Customers: Authenticated SMTP is not enabled by default! Please contact GoDaddy and request that Authenticated SMTP be enabled.

If you are the admin for this account, you can enable IMAP or POP for Office 365:

  • From the Microsoft 365 Admin Center, navigate to Users > Active users > [select a user] > Mail tab > Email apps > Manage email apps link
  • Select IMAP and/or POP, in addition to Authenticated SMTP
  • Click the Save changes button at the bottom

2) Generate an app password for Two-Step Verification

If you are using Two-Step Verification, you must generate an app password for Postbox.

  1. Navigate to the security settings for your Microsoft account at
  2. Scroll down to the App passwords section (which will only appear if you are using Two-Step Verification), and click on Create a new app password.

    Outlook Two-Step Authentication

Use this password in the next step.

3) Ensure that Authentication is set to "OAuth2 - Office 365"

Office365 IMAP and SMTP servers support authorization via the OAuth 2.0 protocol, which Postbox also supports. If you're receiving notifications about using a less secure application or want to use the latest and greatest security protocol, try upgrading your Postbox Office365 account to OAuth2. It's quick and easy to do!

Note: These instructions are only for Office 365 accounts that have already been set up within Postbox.

  1. Within Postbox, navigate to Options | Preferences > Privacy and then select the checkbox for "Accept cookies from sites."
  2. Navigate to Options | Preferences > Security > Passwords > Saved Passwords and click the "Show Passwords" button. Take a screenshot of your passwords, so you have them as a backup.
  3. Remove your Office 365 passwords from the Password Manager, then close the window.
  4. Navigate to Options | Preferences > Accounts. Select the Office 365 account and change Authentication to "OAuth2 (Office365)." Repeat this step for each of your Office365 accounts.
  5. Navigate to Options | Preferences > Accounts > List on the Left > Outgoing Servers. You will want to edit each Office 365 server and change Authentication to "OAuth2 (Office365)."

4) Try disabling IPv6

If you are receiving the following error: "User is authenticated but not connected," please type command-option-shift-8 (macOS) control-alt-shift-8 (Windows) and then paste in: network.dns.disableIPv6

Double-click that row to turn the value to "true," then close the panel and restart Postbox. 

Once complete, restart Postbox, and it will authenticate with each of your Office365 accounts. Use your new app-generated password.

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