Problem

With Microsoft 365 accounts, the 'Authentication Unsuccessful' error can occur when a Microsoft 365 user tries to send emails whilst IMAP is selected as the server type. 

This problem occurs because SMTP authentication is blocked by default for security reasons inside Microsoft 365's settings by any company making use of it. We therefore strongly advise you to use the Exchange protocol which is part of our Business plan to use Microsoft 365 accounts within Mailbird- ultimately, it is much more stable and secure.

Solution

It is still possible to use an IMAP account, but in order to fix the 'Authentication Unsuccessful' error, you need to have Authenticated SMTP enabled in your organization's settings within Microsoft 365. This setting can only be enabled only by the organization's Administrator (either in the 'Microsoft 356 Admin Center' for individual/specific users, or via 'PowerShell' if required for an entire organization).

Please note the following: for GoDaddy Microsoft 365 users it won't be possible to enable SMTP for individual users, but only for the whole organization (via PowerShell) since they do not have access to the 'Microsoft 356 Admin Center'.

Below we will provide some suggested steps in order to enable Authenticated SMTP for a specific/individual account.

1. First, go to the 'Microsoft 365 Admin Center' (https://admin.microsoft.com/)
2. Go to Users and then Active users to select the user for whom you want to enable this setting
3. Then go to Mail, and then Manage email apps
4. Make sure Authenticated SMTP is enabled and then save changes.

In order to enable Authenticated SMTP for an entire organization, here are our suggested steps:

1. First, log into the organization via PowerShell
2. Execute the following "Set-TransportConfig -SmtpClientAuthenticationDisabled $false".

For more details, please take a look at the following useful documentation provided by Microsoft:

• https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission