When you delete an email, it goes into the Trash. It will stay there according to the rules that you set up with your email service. It might stay there for 7 days, 14 days, etc or forever depending on the options that you chose when you set up email.
Now, if you are saying that you deleted the mail that was in the Trash, that is a permanent delete.
However, some email providers have a website where you can view email over the last 30-60 days even though it might have been deleted from the phone.
Check with your email service provider to see if they might have any services like this.