We are getting more and more support requests from people having trouble sending email to Gmail and Google hosted domains. This is currently almost always the result of an email domain not having an SPF record. That is a fairly technical sentence, so click the link for detailed information on SPF. The simplified version is that an SPF record specifies what servers are allowed to send email for your email address. It was designed to help combat spam. If you don’t have one of those records, Google is now rejecting the email with an error message similar to the one below:
host gmail-smtp-in.l.google.com[220.127.116.11] said:
550-5.7.26 The MAIL FROM domain [<your domain>] has an SPF record
with 550-5.7.26 a hard fail policy (-all) but it fails to pass SPF checks
with the 550-5.7.26 ip: [18.104.22.168]. To best protect our users from spam
and 550-5.7.26 phishing, the message has been blocked. Please visit
550-5.7.26 https://support.google.com/mail/answer/81126#authentication for
more 550 5.7.26 information.
In the past, Google would just send the offending message to the Spam folder, but now if the SPF record is missing or fails (as the one above), the message will be rejected.
This can also be caused by “forwards”. For instance, if you have an email address hosted with us, but choose to forward incoming email to a personal Gmail account, you will most likely lose some email as a result of this policy. Senders trying to reach you will receive a failure notice, but there is no way to “fix” this except to check your email in the account rather than forwarding it to another external email address.