Hi Farrell,
You mentioned doing this, "Change the status in CRM for the user be able to send and receive email on behalf of other account ". Is this a business requirement or this was done as part of a default set up?
Are you able to login in any of the test mailboxes ?
Are you able to send test emails from CRM ? (User form >> Send Direct Email)
Are you able to send test emails from that particular mailbox ?
Are both the incoming and outgoing profiles set to use router ?