MS Outlook 365 issuing error 554 6.6.6.0 message

I have 2 laptops running Outlook 365 configured the exact way as best as I can tell.  Both laptops have an account for Exchange Online with a work account and an IMAP account for my personal account.  On the old laptop, I can successfully send an email from the IMAP account to the EOL account without issues.  On the new laptop, I can send an email from EOL to IMAP and reply successfully, however if I try to send an email from IMAP to EOL, the message is immediately rejected with

                554. 6.6.6.0 Error sending message for delivery

I found some references to the error which indicate to change my password on the IMAP account which I have done without success.   How can I find the point of rejection given that I'm successfully able to send from the old laptop.

Any ideas are appreciated.