wlm2012 migrate emails to outlook 2016 (32bit) on Windows 10/64 fails

I have wlm 2012 running on Windows 10/64. Have about 5.5gb of emails to copy across.

Outlook 2016/32 installed and works insomuch as new emails are arriving into it.

However following the procedure for importing emails from wlm2012, I have opened both systems, specify export emails via the microsoft exchange option, the the process starts and then fails after importing 320 of 7500 emails into the inbox (I also do have a number of subfolders which aren't copied across either). tried it twice with the same result.

Okay I've just checked and confirm that the import fails at the point where the external pop3 server is retaining emails (ie set not to delete for 14 says); ie it starts to transfer emails held on the pop3 server first, before falling over.

So three additional questions.

1. Should I delete all emails off the pop3 server first?
2. And/or turn off the internet connection before trying to import emails?
3. Should I call Microsoft as this is a brand new version of Office, only had it 2 days?

Thanks for advice