You need to be logged in to your account and follow the link https://www.instagram.com/download/request 

to check your email address/account registration date or other account information.

Then fill in the required fields and click the “Next” button.

Enter your account password on the next page.

After that, you will receive a link to download your data to the specified email. Follow this link and you will be forwarded to the account menu, where the data download button is available. Download it.

Next, unpack the downloaded archive. There is an index.html file in the archive.
Open it in your browser and you will see all the information about your account.

Check the list of possible email addresses:

• if the list is empty or it contains only the address specified in the package, this is the first/only/original/native email.

• if there are other addresses in the list and they differ from those specified in the package, the current email address is NOT the original one.