Yes, Exporting mails to PST is available through the self service portal.
If you opt for the DURABILITY plan of Vaultastic, you can import legacy mail data into the archive accounts of the users. The method of doing this will vary depending on the source platform and we offer this as a service. If it requires us to do a PST import, we may do that too.
Refer the link How to choose plan for users on Vaultastic