Some emails vanish but not all

Emails randomly vanish from inbox. Not all, just some. Very annoying indeed.

Hello Vivien,Could you please specify few details? On which account this happens? Is it possible that you have set automatic archiving for your inbox folder?Thank you.

Accounts - both mine and my husbands. Automatic archiving off. This email from you disappeared from Em Client, I had to revert to Windows Live Mail to retrieve it.