Sub-Folder in Mail / Macbook Air

I am using the MacBook air.

I have a problem in creating a sub-folders in MacBook. Where after I create a folder, then try to create a sub-folder of it, a window will pop up asking the name of the sub-folder BUT it will be under the Hotmail! and not under the new folder that I created.

Before that time, when this problem happened, normally I quit or force to quit the mail app and reopen it again and then the sub-folder can be created under the new folder that I want it to be. But recently this step does not work aymore.

Please advise:-

1-Is there any limit for the numbers of the folders that we can create in (on my Mac) mail app?

2-Is there any limit for the numbers of the sub-folders that we can create under a folder in (on my Mac) mail app.?

3-How can I solve the problem of creating a new sub-folder under new generated folder in (on My Mac)?

Thank you