Thanks a lot burnout426!!!

I followed your suggestions and I was able to recover completely my mail database. It took time (hours) for old accounts with a lot of messages (of many years) but it worked.

It was also an opportunity to reorganise (simplify) a few email accounts (in particular, I imported into a single mail account the email messages from several related accounts that are now closed / dismissed and derived from from past working experiences. Apparently it worked nicely)

New contacts were automatically created from the imported messages. Thus, I was able to work immediately, at least with the most used email addresses.
I am now trying to make a comparison with the file "contacs.adr" I saved before the restructuring, to see if something is missing or named differently.

Thanks.

Many thanks for the long and accurate answer. I will take the time to follow carefully your suggestions.

Just to summarize after a quick reading: it is possible to re-build the database for all accounts but additional labels etc. Are lost (or much more difficult to restore).

Apparently, the news is good for me as I will be able to search and find previous messages

Thanks again, I will let you know the final outcome
Giuseppe

I am using OperaMail with a very large mail "database" (messages since 2008, 28GByte) and about ten different email accounts.
Last week I switched smoothly from Windows 8.1 to Windows 10.

Yesterday, I saw a "hardware failure" message from Windows and since the PC restarted, Opera Mail shows only 8 (eight) messages (rather "randomly" selected: 2 in June 2015 and 6 in August and December 2014). I did not notice other problems and I am still able to send and receive emails with all my accounts using Opera Mail.

In addition, the mail folder (in C:\Users\Pino\AppData\Local\Opera Mail\Opera Mail\mail) still contains all .mbs files organised into the store subfolder (for accounts, years, months and days).

I do not know if the the "hardware failure" is related to the problem but my question is:
How can I force Opera Mail to see all mail messages (contained in the mail folder)?

Thanks
Giuseppe