Order e-mails are marked as spam in customer inbox

[Peter Pillen]

joomla 2.5.8
virtuemart 2.018a

I just tested and got confirmation with a few accounts that I used to place testorders to see how the order e-mails are handled. And I noticed that in gmail for example, all my order invoices are flagged as spam automatically. I saw a lot of post that say: use smtp (tried that), make a spf record (not easy), and so on.

What is the best solution? I already learned that a correct e-mail header needs to be set but the order email says

From: MyCompany <peter@mycompany.com>
Reply to: MyCompany <peter@mycompany.com>
sent to: peter@gmailtest.com

but when I click on reply, the Send to field in the reply e-mail is filled in with "peter@gmailtest.com" and not "peter@mycompany.com". So the customer just sends an e-mail to himself 

According to some sources this is not correct for most mailing programs.