Why is it not advisable to manually import PST files?
If the PST migrations will be done by hand, then this can be done. It might make sense for small accounts, but it would be too time-consuming for large migration projects.
To do it by hand, import the PST file into the Office 365 mailbox, from within the end user's Outlook client. This essentially imports the PST file into the .ost file that is stored on that client. Once imported into the .ost file, it would then get synched up to Office 365 so that all the email would be included in the mailbox.
Here is a Microsoft Technet article that provides more information: Import email, contacts, and calendar from an Outlook .pst file.
Note: It would be possible to simply reattach the PST file into their Outlook client, but this creates a problem in that they, of course, wouldn't be able to access those emails that are in the PST file from other clients, or through OWA. In addition, PST files have a tendency to get corrupted over time (another big reason for PST file migrations).
There are a couple more reasons why it is generally not a good idea to manually import PST files into users' mailboxes, for large projects:
- The end users will experience downtime while the engineer is importing the PST files.
- The engineer will also have to do this for all of the end users, which is time-consuming.
Also, rather importantly, the x500 addresses within the PST file will not be able to be replied to.
To be more clear: X500 addresses are those addresses that are internal to a company. Therefore, if an email that was in the PST file is imported into the .ost file, and then synched so that it is held in the Office 365 mailbox, then that email will be impossible to reply to, using that x500 address. In order to make it available to be replied to, it would be necessary to delete the x500 address and then enter in a fresh, new "to" address.
Note: Our PST migration tool converts those x500 addresses into SMTP addresses. Read the article Will MigrationWiz ensure migrated emails are can be replied to? for more information.