Migration error: "The server cannot service the request right now" (4241619)

If Microsoft EWS throttling has not been relaxed you may see the following warning when migrating mailbox data.

The server cannot service the request right now.  Try again later.  Waiting 5.00 minutes before resuming.

"[1/3]Error detected, attempting retry 1 of 5
An existing connection was forcibly closed by the remote host
(An existing connection was forcibly closed by the remote host)"
"[2/3]Error detected, attempting retry 1 of 5
An existing connection was forcibly closed by the remote host
(Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.)"
"[3/3]Error detected, attempting retry 1 of 5
An existing connection was forcibly closed by the remote host
(The request failed. Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.)"

Exception of type 'Quest.Rest.RestException' was thrown.; WebStatus = Success; StatusCode = ServiceUnavailable; StatusDescription = 'Service Temporarily Unavailable'; Content = ''

or

"Waiting for Microsoft Azure to send the response back, The server cannot service this request right now. Try again later. waiting 0.00 minutes before resuming"

"Response status code does not indicate success: 403 (Site Disabled).
(Response status code does not indicate success: 403 (Site Disabled).)"

Error creating source session. Response status code does not indicate success: 403 (Site Disabled).(Response status code does not indicate success: 403 (Site Disabled).)

You can increase the throttling for your source and target tenants by following the directions  below.  

• Logon to the Office 365 portal
• Click Admin icon to open the admin center
• Click on the ? on the top right
• Click in the text field and search “EWS throttling”
• Click the Run Tests button
• If EWS is being throttled a prompt will be displayed to select the number of days to relax throttling.  The max setting is 90 days per request.
• Click the acknowledgement checkbox
• Click the Update Settings button

When the settings are updated the following message will be displayed.