Windows is decommissioning mail protocol APIs

[DelJo63]

Today, we are announcing that on October 13th, 2020 we will stop supporting and retire Basic Authentication for Exchange Active Sync (EAS), Post Office Protocol (POP), Internet Message Access Protocol (IMAP), and Remote PowerShell (RPS) in Exchange Online. This means that new or existing applications using one or more of these API’s/protocols will not be able to use Basic Authentication when connecting to Office 365 mailboxes or endpoints and will need to update how they authenticate.

Here's the announcement.