Microsoft has announced, that they are disabling basic auth on October 1st, 2022 for all tenants. It doesn‘t matter if you use it now or not. It gets disabled after October 1st, 2022.
From the announcement post:
Today, we are announcing that, effective October 1, 2022, we will begin to permanently disable Basic Auth in all tenants, regardless of usage (with the exception of SMTP Auth, which can still be re-enabled after that).
How is this relevant to our Veeam Backup Office 365 Installations?
Today, Veeam can backup Office 365 data without basic auth (modern Auth Only).
But this has some limitations. You can find them in this post:
As soon basic auth is disabled from Microsoft, vbo servers with organizations and „modern authentification with legacy protocols“ or „basic authentication method“, backup jobs will most likely stop working.
What can be done from us administrators?
Everyone should be ready for this change when it happens. Perhaps, veeam will write a kb until next year to inform customers what can be done for vbo365.
For me, I think we will change to modern auth only and inform our customers about the new limitations. We will decide next summer when it gets clearer, what needs to be done. Security is more important than most of the missing features.
What other Third Party Software could be affected?
I have seen old software with POP3 Integration which are using POP3 with Basic Auth. They need to be checked if they can work with Modern Auth.
Software, which uses the EWS API from Microsoft needs also to be able to use Modern Auth. There are many software on the market with calendar integration which are connecting only with Basic Auth, to get the users calendars data.
SMTP will not be affected as written in the Microsoft Announcement Post.
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I am looking forward to October 2022 and what doesn‘t work after that. 
