If migrating to Office 365 from a platform which previously used POP3, there will be a need to import all users email history into Office 365. As POP3 email is downloaded to the clients machine and this is where it all stays for the duration of it's life they traditionally get VERY BIG! In a recent migration they hav ranged from 1GB to over 30GB each.
Office 365 actually have a solutution for this, but it's not well advertised. You have to install a small client on your uploading device, log into the tenant account and then you can see the "Import" button as shown here,Steps for Bulk PST import in Office 365
1. Populate the CSV File Provided with all of the PSTs you need to import.O365PstImportMappingFile.csv (188B)
2. Apply the import/export permissions to the tenant account.Excahnge GUI > Permissions >
Select "Organization Management"
and click Edit >
click on the plus symbol to "Add a role" >
Select Mailbox Import Export
and OK to confirm the changes.
3.Log in to the Tenant account (not as a pertner) > Import
> Upload files over the network
4.If not already done, Install Microsoft Azure Storage Tool with the link provided on this screen.
5. Copy the storage key and URL. KEEP THEM SAFE.
6. Start Azure Storage Tools and run:
AzCopy.exe /Source:<Source local location of PST> /Dest:"<SASURL + Folderlocation + SAS Key>" /V:AzCopylog.txt
AzCopy.exe /Source:C:\PST /Dest:"https://9b0867cef3123456659d0ed34.blob.core.windows.net/ingestiondata/PST?sv=2012-02-12&se=2016-10-09T10%3A56%3A45Z&sr=c&si=IngestionSasForAzCopy201612478032551098&sig=x5mzZ21UrIGptiVXOGl5a9A1d31PUcAFLwJjvOCOcXA%3D" /V:AzCopylog.txt
Everything in /Dest: and /DestSAS:needs to be in inverted commas
7. Once this is complete you can click next on the "Upload files over network" windows after checking the two check boxes.
8. Upload and validate the CSV file
9. Watch your PSTs import!
You can see all the details reporting from the Office 365 console including failed copies etc.