If you remember since 2019, Microsoft has been announcing the retirement of Basic Authentication in a way to improve security as Basic Authentication does not support multi factor authentication (MFA) (see https://t.co/9XZtsVFoQr).
Well, Office 365 and Exchange Online administrators should start looking at their Message Center has the retirement is starting and Microsoft provides you specific information if their telemetry shows you are still using it.
On my tenant, the Message Center ID is MC336598 (it may be different in your tenant); extract of the message below
7 days from today we’re going to turn off Basic Authentication for POP3 protocol in your tenant. Based on our telemetry, no-one is currently using Basic Authentication with that protocol in your tenant and so we expect there to be no impact to you.