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Google’s Gmail might be the preeminent mailbox provider. Launched in 2004, Gmail has grown from the “new kid on the block” into one of the biggest hosts of individual email mailboxes in the world. Depending on what data you look at, you might even see Gmail as the #1 mailbox provider, at least here in the US. Gmail’s spam filtering systems incorporate user feedback and engagement. And they know what they’re doing. If you are not sending wanted mail to people who requested that mail and who read that mail at high enough percentages, you’re going to struggle. You won’t reliably get your mail to the inbox. Their systems are too good — their magic spam fighting robots look at metrics very closely — and their view of certain metrics can even change over time! What got you to the inbox in 2019 might not be good enough to get
A few days ago, Google started notifying (some) Google Workspace customers of updated spam filter/blocking changes coming to the Gmail email service. They’re moving to more proactively block emails that have headers violating RFC 5322, and it is believed that this is an attempt to help prevent DKIM replay attacks. Read on to learn more about what this means and how it could impact email senders.In the notification below, they indicate that they’ve sent this only to Workspace users they think may be impacted by this change, but truth be told, it affects the entire internet, as it could impact anyone sending email messages to any user at a Google-hosted mailbox.The notification: We’re writing to let you know about an upcoming change to your Gmail services. Gmail will start rejecting messages that are non-compliant with Internet Message Format standards and contain more than one single-instance email header as of April
Here is the scenario. Maybe you’ve just gotten a bounce message that looks like this:Aug 25 11:20:24 s1 postfix/smtp[26906]: 98299221BB: to=, relay=gmail-smtp-in.l.google.com[142.250.141.27]:25, delay=1.2, delays=0.04/0.77/0.2/0.21, dsn=5.7.1, status=bounced (host gmail-smtp-in.l.google.com[142.250.141.27] said: 550-5.7.1 [206.125.175.2] Our system has detected that this message is not RFC 550-5.7.1 5322 compliant: duplicate headers. To reduce the amount of spam sent 550-5.7.1 to Gmail, this message has been blocked. Please review 550 5.7.1 RFC 5322 specifications for more information. j6-20020a637a46000000b0042b3a763e76si3563504pgn.127 – gsmtp (in reply to end of DATA command))Or perhaps it looks like this:Aug 25 12:48:59 s1 postfix/smtp[14180]: C90492056B: to=, relay=aspmx.l.google.com[142.250.141.27]:25, delay=0.69, delays=0.08/0/0.39/0.22, dsn=5.7.1, status=bounced (host aspmx.l.google.com[142.250.141.27] said: 550-5.7.1 [206.125.175.2] Our system has detected that this message is not RFC 550-5.7.1 5322 compliant: 550-5.7.1 Multiple ‘From’ headers found. 550-5.7.1 To reduce the amount of spam sent to Gmail, this message has been 550-5.7.1 blocked. Please visit 550-5.7.1 https://support.google.com/mail/?p=RfcMessageNonCompliant 550 5.7.1 and review RFC 5322 specifications for more information.