If you are using multiple Hotmail/Outlook accounts with forwarding set up, and one of them gets upgraded to the Preview version of a new Outlook.com you may be losing mail.

Microsoft is incorporating a new version of Outlook into Office365 and has changed some Hotmail/Outlook accounts to the new, preview, version. All of a sudden, some of my correspondents were telling me all their e-mail to me was being returned. It turned out it was the e-mail addressed to the account which was upgraded.

I contacted MS support last weekend and after a really great telephone session with one of their engineers and using one of my correspondents sending test e-mails, we found that the preview account was receiving the e-mail properly, but when it tried to forward it to the "master" account, that account did not recognize the preview account and marked the e-mail as undeliverable. Unfortunately, as the preview account set up the forwarding, it did not keep a copy of the e-mail, as designed. After all, it should be in the master account. That meant all trace except the undeliverable notice was lost.

We also determined that reversing the roles of the two accounts still failed to make the forwarding work. There is no "promise date" for correcting this known deficiency.

I suspect rather than correct this situation they will accelerate the conversion to the new Outlook.com version. Until that happens, forwarding will only work when between accounts using the old Hotmail/Outlook or between accounts using the the Preview version of the new Outlook.com. And you will lose any mail which one type of account tries to send to the other. The only current solution appears to be to treat each type of account separately until all Hotmail/Outlook accounts are running the same versions and delete any forwarding set up between incompatible accounts.