Email Spam

Hi

When a client buys a product from my site, an email is sent automaticly to them.

This has directions how the client can get the product.

Unfortunately, some messages are ending up in their spam folders.

This is ok if the client is PC savvy because they know where to look.

However, if they are not, they get worried that they have paid but not received anthing.

Is there a way to ensure the mail reaches them?

What are the best practices to prevent this problem

Thanks