Many migration projects use Exchange Web Services (EWS) to move data to Exchange Online. EWS is using throttled to preserve resources. Here’s how to lift the restrictions for up to 90 days, all without going near a support call.
Microsoft has announced that basic authentication for multiple email connection protocols won’t be supported after October 13, 2020. You won’t be able to connect with EWS, EAS, IMAP4, POP3, or Remote PowerShell unless you use modern authentication. There’s just over a year to prepare, but there’s some work to be done.