Gmail Postmaster Tools provides senders with metrics on parameters such as reputation, spam rate, feedback loop, etc. It can help you check compliance to the Gmail bulk sender guidelines, as well as identify issues that can cause trouble with the spam filter.

We've received inquiries from bulk senders who'd like more information on best practices to ensure that their mail is delivered to Gmail users. Gmail classifies incoming mail in the following ways:

• Spam vs. non-spam: Spam messages are placed in the spam folder, while non-spam message are placed in the inbox.
• Mail categories: Most users use Gmail's default inbox which further classifies non-spam mail into categories – Primary, Social, Promotions, Updates and Forums. Primary, Social and Promotions are enabled by default, but users can choose to enable or disable from all five to none. The Primary category includes person-to-person conversations and message categories that aren't currently enabled.

Mail classifications depend heavily on reports from users. Gmail users can mark and unmark messages as spam, and can move non-spam messages between inbox tabs. In both cases Gmail learns from user corrections and over time automatically adjusts the classification to match users’ preferences.

The following guidelines can help you achieve predictable classification and receiver satisfaction.

Inbox classification

Inbox categories

Spam classification

Authentication & Identification
Subscription
Unsubscribing 
Format
Delivery
Third-Party Senders
Affiliate Marketing Programs
 

Not in the right place?

• If you received an error message when sending an email to a Google Apps group, click here.
• Just sending mail to a friend or business associate? Click here for further help.

Gmail’s inbox categories help users organize and better control their inboxes by classifying mail into categories and putting mail from those categories into tabs.

Users can choose to have specific messages or senders always go to a particular category and can switch each category to be on or off. Starring a message will put it in the Primary category. Gmail learns from user corrections and over time automatically adjusts the classification to match users’ preferences.

Here’s what you can do to help Gmail categorize your messages correctly:

• Send different categories of mail (e.g. promotions, transaction notifications, social updates) from different sender addresses, and try to keep those addresses consistent over time.
• Avoid mixing different categories of content in one email. For example, putting a promotion into a transactional mail notification may make the system classify the message as promotional.

To ensure that Gmail can identify you:

• Use a consistent IP address to send bulk mail.
• Keep valid reverse DNS records for the IP address(es) from which you send mail, pointing to your domain.
• Use the same address in the 'From:' header on every bulk mail you send.

We also recommend the following:

• Sign messages with DKIM. We do not authenticate messages signed with keys using fewer than 1024 bits.
• Publish an SPF record.
• Publish a DMARC policy.

  Learn more about email authentication.

  Additional guidelines for IPv6
  

   

  Subscription

  Each user on your distribution list should opt to receive messages from you in one of the following ways (opt-in):

  We also recommend that you verify each email address before subscribing them to your list.

  The following methods of address collection are not considered 'opt-in' and are not recommended:

   

  Unsubscribing

  A user must be able to unsubscribe from your mailing list through one of the following means:

  Because Gmail can help users automatically unsubscribe from your email, we strongly recommend the following:

  To help ensure that your messages aren't flagged as spam, we also recommend that you:

  It's possible that your users forward mail from other accounts, so we recommend that you:

   

  Format

   

  Delivery

  While Gmail works hard to deliver all legitimate mail to a user's inbox, it's possible that some legitimate messages may be marked as spam. Gmail does not accept 'whitelisting' requests from bulk senders, and we can't guarantee that all of your messages will bypass our spam filters. To make sure our users receive all the mail they'd like to, we've provided them with a method for sending us feedback about messages flagged as spam — users have the option of clicking a 'Not spam' button for each message flagged by our spam filters. We listen to users' reports, and correct problems in order to provide them with the best user experience. As long as our users don't consider your mail as spam, you shouldn't have inbox delivery problems.

  There are two important factors that, under normal circumstances, help messages arrive in Gmail users' inboxes:

  If you send both promotional mail and transactional mail relating to your organization, we recommend separating mail by purpose as much as possible. You can do this by:

  By using these tips, it's more likely that the important transactional mail will be delivered to a user's inbox. Our guidelines are meant to help you build a good reputation within the Gmail system, resulting in continual delivery to Gmail inboxes.

   

  Third-Party Senders

  If others use your service to send mail (for example: ISPs), you are responsible for monitoring your users and/or clients' behavior.  

   

  Affiliate Marketing Programs

  Affiliate marketing programs reward third-parties for bringing visitors to your site. Unfortunately, these programs are attractive to hard-core spammers and can potentially do more harm than good. Please note the following:

  
  If you are sending mail in accordance with our guidelines and Gmail continues to mark your messages as spam,troubleshoot further.

  • • The sending IP must have a PTR record (i.e., a reverse DNS of the sending IP) and it should match the IP obtained via the forward DNS resolution of the hostname specified in the PTR record. Otherwise, mail will be marked as spam or possibly rejected.
    • The sending domain should pass either SPF check or DKIM check. Otherwise, mail might be marked as spam.
    • Through an email asking to subscribe to your list.
    • By manually checking a box on a web form, or within a piece of software.
    • Using an email address list purchased from a third-party.
    • Setting a checkbox on a web form or within a piece of software to subscribe all users by default (requiring users to explicitly opt-out of mailings).
    • A prominent link in the body of an email leading users to a page confirming his or her unsubscription (no input from the user, other than confirmation, should be required).
    • By replying to your email with an unsubscribe request.
    • Provide a 'List-Unsubscribe' header which points to an email address or a URL where the user can unsubscribe easily from future mailings. (Note: This is not a substitute method for unsubscribing.)
    • Automatically unsubscribe users whose addresses bounce multiple pieces of mail.
    • Periodically send confirmation messages to users.
    • Include each mailing list they are signed up for, and offer the opportunity to unsubscribe from those in which they are no longer interested.
    • Explicitly indicate the email address subscribed to your list.
    • Support a URL method of unsubscribing from your mailing list (this is beneficial if your mailing list manager can't tell who is unsubscribing based on the 'Reply-to:' address).
    • All messages must be formatted according to RFC 5322 and, if using HTML, HTML standards.
    • Messages must have a valid 'Message-ID:' header field.
    • Messages should indicate that they are bulk mail, using the 'Precedence: bulk' header field.
    • Attempts to hide the true sender of the message or the true landing page for any web links in the message may result in non-delivery.
    • The subject of each message should be relevant to the body's content and not be misleading.
    • The authenticating domain, envelope From domain, payload From domain, reply-to domain, and sender domain should not violate the highly-restrictive Unicode Security Profile guidelines for international domain names.
    • The 'From:' address is listed in the user's Contacts list.
    • A user clicks 'Not Spam' to alert Gmail that messages sent from that address are solicited.
    • Using separate email addresses for each function.
    • Sending mail from different domains and/or IP addresses for each function.
    • You must have an email address available for users and/or clients to report abuse ([email protected]).
    • You must maintain up-to-date contact information in your WHOIS record, and on abuse.net.
    • You must terminate, in a timely fashion, all users and/or clients who use your service to send spam mail.
    • If your brand becomes associated with affiliate marketing spam, it can affect the mail sent by you and your other affiliates.
    • It is your responsibility to monitor your affiliates and remove them if they send spam.