First off, I did not want to buy any third-party product to do a mail migration from Outlook (local .pst) into a shiny Lotus Notes 8.5.1 .
When doing some test to migrate Outlook 2007 messages (local .pst), I luckly realize that all messages were migrated BUT they LOST their attachments...
I opened a ticket with IBM Support and after some days a polite guy gave me the hint:
add a special notes.ini setting inside the Notes I was migrating all message.
The "abracadabra sentence" is: ExchMig_ConAllAtt=1
After I got the solution I did a search on the Web for the special notes.ini setting (worth mentioning Andy's post and comments) and it seems that the problem is not new at all, it's coming up every now and then since version 7 and later.
I EXPECT that IBM / Lotus migration tools will work perfectly, especially when the previous mail system is the main competing mail system, MS Outlook.
I really wish nupgrade.exe tool will be soon updated to smooth the mail migration.