The sync process will only sync eMails where the eMail address is 'known' to Access Recruitment CRM.
It will not sync eMails if the saved eMail address has a space at the front (which can happen if the eMail is pasted)
The Sync process keeps a track of the date a folder is synced and uses that to filter the email created/update from the last sync.
Individual eMails are also tracked to prevent duplicates.