A ServerBusyException indicates that the server SmarterMail was pulling information from was too busy to respond to a request for data. Because this is not an unusual exception to receive, SmarterMail will wait a few minutes after receiving a ServerBusyException before continuing to retrieve the affected folder. The amount of time between attempts is dependent on the consecutive number of attempts that result in a ServerBusyException. If 5 consecutive requests result in a ServerBusyException, SmarterMail will move on to the next folder.

This means that, in most cases, a ServerBusyException is not a concern. However, if the logs show 5 ServerBusyExceptions for the same folder, it might be an indication that the folder was not fully retrieved.

THX Andrew, so in my case this is a "good log" and all the data should be migrated, am I right?