The IMAP Sync option can only be used if the mail to be migrated resides in an IMAP mailbox. To help you decide on the best strategy for you, refer to the www.vaultastic.com/migration page.
The HDU can inform you on the number of mail in Vaultastic after sync. It will not be able to identify the exact mail which did not get synced.
In some rare cases, the conversion tool may not be able to convert source mail files to a Vaultastic compatible format. In such a case the mail will be skipped.
If a failed job is restarted, there will be no duplication. However if a processed job is resubmitted with the same destination folder, then there will be mail duplication on Vaultastic.
HDU supports all IMAP servers and has been tested with GSuite, O365 and SkyConnect. If you need support for other IMAP servers, do contact us and we would be happy to help.
The HDU applies no limits on the size of the mailbox being migrated.