Prevent company emails going to Spam folder of the customers.

Hi,
We are using a software developed with Delphi which is sending emails at the end of the day to the customers informing them about their order.

Loads of customers are complaining they haven't recevied their emails and when I tell them to check their Spam Folder, 80%, they find the email there.

I am using IP Works HTML emailer.is there any way to stop our emails going to spam folders? couple of tricks in the header of the email for example?

Regards,
Bill