Mail disappeared from folders - again.

I use an iPad 7 gen running iPadOS 18.6

I use outlook for e mails & access it via the Mail icon.

For years I have created folders in my mail account to keep important e documents, insurance,holidays etc etc.

I now find all my folders are completely empty & important information lost.

I also have an iPhone & they have disappeared there as well .

This is the second time it’s happened, the first being a few years back.

I believe I tried this forum then but had no luck.

Does anybody know why this happens & if it’s possible to retrieve the lost mail?

Would appreciate any answers in plain English as my knowledge of these devices is limited due to advanced age !

Thanks