Whenever I open Outlook I get the following message:
The data file was not closed properly. This file is being checked for problems.
… and suddenly many spam mails arrive in my mailbox.
This message appears if last time outlook not closed properly, kindly complete the scan and reopen outlook. It should resolve your problem, other wise Scan PST is good free tool to repair PST file.
I would do export of all personal folders (incl. subfolders) to new .pst file.
File -> Open -> Import -> and select "export to file"
Then not import, but add exported.pst file to outlook as second one, set it as default, set it as default for your account and then remove the original one.
File -> Info -> Account Settings In "Account Settings" go to tab "Data Settings" and "Add" exported.pst Set it as default On tab E-mail, then select Inbox for your Account from exported.pst