Outlook mail automatically disappeared in my Android device

Can you please give more information about your issue? Namely things like:
- what version of Android are you using?
- what mail app are you using (I presume it's Outlook but want to confirm)?
- does this always happen, or is it recent, or just in a specific circumstance?

I would also suggest choosing the support option from within the Outlook app as that will connect you directly to the product support team, whereas this is a community forum where technical support is not guaranteed.