What are “must have” headers to ensure your email will make it to most inboxes? For example, I get messages fine in my Gmail account but a friend had a message go to their Gmail spam folder.
The only one I’m using now is “From: $name <$email>”
Thanks!
Here is a good introduction on things you should do to avoid being seen as spam: http://mailchimp.com/resources/guides/how-to-avoid-spam-filters/html/
As for the headers, you may want to look into SPF and DKIM. Both use a combination of email headers and DNS records to verify that you are allowed to send email from the domain you’re sending from. SPF is relatively painless to install, but DKIM is quite hard. Your best chances of staying out of spam boxes are if you use both.
If you are sending a lot of email it may be wise to outsource sending email to a service like SendGrid or Amazon SES, who deal with all this stuff for you so you don’t have to think about it; you just send the contents of the email and they make sure they do all they can to get it to the inbox of the recipient.