Today I noticed that Gmail sends all messages received from my server to the Spam folder. I checked message header and found the following:
Authentication-Results: mx.google.com; spf=neutral (google.com: 2001:4ba0:cafe:........ is neither permitted nor denied by best guess record for domain of email@example.com) firstname.lastname@example.org
So, it looks that Sendmail is sending mail from IP6 adress insrtead of IPv4 and there is no SPF and PTR records for IPv6. How do I force Sendmail to send mail from IPv4?