missing email

I have lost my old emails that were stored in my inbox. I can only see emails from 4 weeks ago.

I had emails stored since 2007. For mails that I had saved in a folder I can still see them. I can also see all my old sent emails

I have not physically deleted these emails. I only noticed today but have had problems searching for emails over the past few weeks.

I use a mobile device, but have not had any issues with this in the past

This is a real problem for me as I have flight details and other travel details on these emails

Please advise me what to do asap

Question about Outlook Express