I have a website in a Linode VPS in Linode.
The email address to receive emails is hosted in Google Apps, but I send emails from postfix.
For that to work and not cause problems with spam folders, I have created this SPF record:
v=spf1 include:_spf.google.com ~all
Unfortunately all email gets into the spam folder, especially on Hotmail.
Reading guides and answers here in serverfault, I concluded that I need to add the ip4 info in my SPF record, like this:
v=spf1 ip4:xxx.xxx.xxx.xxx include:_spf.google.com ~all
My emails contain a header image, that is loaded remotely from the same domain. Obviously ISPS hide automatically this image, but is it a factor to classify the email as spam? Do I need anything else taking into account my setup? Is DKIM absolutely necessary?