(Google) A sentence about the ARC authentication added at Email Sender Guidelines: https://support.google.com/mail/answer/81126

Author: azumakuniyuki

google-81126-email-sender-guidelines.txt

@@ -78,9 +78,9 @@ follow the Requirements for sending 5,000 or more messages per day.
     spam rates
   • Format messages according to the Internet Message Format standard, RFC 5322
     .
-  • Don’t impersonate Gmail From: headers. Gmail will begin using a
-    DMARC quarantine enforcement policy, and impersonating Gmail From: headers
-    might impact your email delivery.
+  • Don’t impersonate Gmail From: headers. Gmail will begin using a DMARC
+    quarantine enforcement policy, and impersonating Gmail From: headers might
+    impact your email delivery.
   • If you manage a forwarding service, including mailing lists or inbound
     gateways, add ARC headers to outgoing email. ARC headers indicate the
     message was forwarded and identify you as the forwarder. Mailing list
@@ -136,7 +136,7 @@ Authenticated messages:
 
   • Help protect recipients from malicious messages, such as spoofing and
     phishing messages.
-  • Help protect you and your organization from being impersonated. 
+  • Help protect you and your organization from being impersonated.
   • Are less likely to be rejected or marked as spam by Gmail.
 
 Set up email authentication for each of your sending domains at your domain
@@ -148,7 +148,7 @@ to Gmail accounts. To improve email delivery, we recommend that you always set
 up SPF, DKIM, and DMARC for your domains. Make sure you're meeting the minimum
 authentication requirements described on this page. Messages that aren’t
 authenticated with these methods might be marked as spam or rejected with a
-5.7.26 error. 
+5.7.26 error.
 
 If you use an email service provider, verify that they authenticate your
 domain’s email with SPF and DKIM.
@@ -201,6 +201,10 @@ ARC checks the previous authentication status of forwarded messages. If a
 forwarded message passes SPF or DKIM authentication, but ARC shows it
 previously failed authentication, Gmail treats the message as unauthenticated.
 
+When ARC shows that a forwarded message previously passed authentication, Gmail
+doesn’t automatically authenticate the message. Instead, Gmail does its own
+authentication check on the message.
+
 We recommend that senders use ARC authentication, especially if they regularly
 forward email. Learn more about ARC authentication.
 
@@ -209,7 +213,7 @@ Infrastructure configuration requirements and guidelines
 IP addresses
 
 Important: The sending IP address must match the IP address of the hostname
-specified in the Pointer (PTR) record. 
+specified in the Pointer (PTR) record.
 
 The public IP address of a sending SMTP server must have a corresponding PTR
 record that resolves to a hostname. This is called a reverse DNS lookup. The
@@ -234,7 +238,7 @@ If you use a shared IP address for sending email:
 
   • Make sure the shared IP address isn’t on any internet blocklist. Messages
     sent from IP addresses on a blocklist are more likely to be marked as spam.
-  • If you use an email service provider for your shared IP,  use Postmaster
+  • If you use an email service provider for your shared IP, use Postmaster
     Tools to check the reputation of the shared IP address.
 
 Subscription requirements and guidelines
@@ -261,7 +265,7 @@ Make it easy to unsubscribe
 
 Always give recipients an easy way to unsubscribe from your messages. Letting
 people opt out of your messages can improve open rates, click-through rates,
-and sending efficiency. 
+and sending efficiency.
 
 Important: If you send more than 5,000 message per day, your marketing and
 subscribed messages must support one-click unsubscribe.
@@ -325,7 +329,7 @@ delivered as expected:
       □ Sender information should be clear and visible.
   • 
   • Format the following international domains according to Section 5.2 of
-    Unicode Technical Standard #39. An international domain is also called an 
+    Unicode Technical Standard #39. An international domain is also called an ;
     internationalized domain name (IDN), and is a URL that is specific to a
     region or country.
       □ Authenticating domain
@@ -398,11 +402,10 @@ If you send large amounts of email, we recommend you:
   • Send email at a consistent rate. Avoid sending email in bursts.
   • Start with a low sending volume to engaged users, and slowly increase the
     volume over time.
-  • As you increase the sending volume, regularly monitor server
-    responses, spam rate, and the sending domain's reputation. Regular
-    monitoring will allow you to quickly adapt if your sending is rate limited,
-    if the spam rate is increased, or when the sending domain's reputation
-    drops.
+  • As you increase the sending volume, regularly monitor server responses,
+    spam rate, and the sending domain's reputation. Regular monitoring will
+    allow you to quickly adapt if your sending is rate limited, if the spam
+    rate is increased, or when the sending domain's reputation drops.
   • Avoid introducing sudden volume spikes if you do not have a history of
     sending large volumes. For example, immediately doubling previously sent
     volumes suddenly could result in rate limiting or reputation drops.
@@ -505,7 +508,7 @@ Spam rate
   • Regularly monitor your domain's spam rate in Postmaster Tools.
 
   • Keep spam rates reported in Postmaster Tools below 0.10% and avoid ever
-    reaching a spam rate of 0.30% or higher. Learn more 
+    reaching a spam rate of 0.30% or higher. Learn more
   • Maintaining a low spam rate helps senders be more resilient to occasional
     spikes in user feedback.
   • Maintaining a high spam rate leads to increased spam classification. It can