Emails without authentication often get rejected or marked as spam to protect recipients from phishing scams. Unauthenticated emails with attachments might get completely rejected for security reasons.

To ensure Gmail can authenticate you:

• Send from the same IP address
• Keep valid reverse DNS records your IP address that points to your domain
• Choose the same address in the 'From:' header for every bulk message

Other recommendations

• Sign messages with DKIM. We don't authenticate messages signed with keys that use fewer than 1024 bits.
• Publish aanSPF record.
• Publish a DMARC policy.

Learn more about email authentication.

IP guidelines

• The sending IP must have a PTR record (i.e. a reverse DNS of the sending IP) and match the IP obtained via the forward DNS resolution of the hostname specified in the PTR record.
• The sending domain should pass either an SPF check or DKIM check.

1. Provide each recipient on your distribution list either "opt-in" option below:
   • An email asking them to subscribe
   • A checkbox on a web form or in the software they need to manually check
2. Confirm each recipient's email address is correct before subscribing them.
3. Avoid:
   • Purchasing an email address from a third-party
   • Including a checkbox on a web form or in software that is automatically checked and subscribes users by default

Make sure your messages have:

• Formatting according to RFC 5322 and, if using HTML, HTML standards
• A valid 'Message-ID:' header field
• An indication that you're sending bulk mail in the 'Precedence: bulk' header field
• Visible information about the true sender and true landing page for links
• Subject lines that are relevant to the message content and not misleading
• Domain formatting according to the highly-restrictive Unicode Security Profile guidelines for international domain names, including:
  • Authenticating domain
  • Envelope From domain
  • Payload domain
  • Reply-to domain
  • Sender domain

Important factors for delivery

While Gmail works hard to deliver all legitimate mail, it's possible that some legitimate messages get marked as spam.

Here are factors that normally help deliver messages to Gmail recipients:

• The 'From:' address matches someone in the recipient's Contacts
• If your message is welcome but accidentally sent to spam, the recipient can click Not spam

Note: Gmail doesn't accept 'whitelisting' requests from bulk senders, and can't guarantee that all of your messages will bypass our spam filters.

Promotional mail or financial transactions

To help improve the chances of getting important promotional or transactional mail to your recipient, we recommend separating mail by purpose as much as possible. For each type of mail (promotional or transactional), you can:

• Use separate email addresses
• Send mail from different domains and/or IP addresses

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

• Provide an email address to your users and/or clients to report abuse (for example, abuse@yourdomain.com)
• Maintain up-to-date contact information in your WHOIS record and on abuse.net
• Quickly terminate all users and clients who use your service to send spam

Affiliate marketing programs reward third-parties for bringing visitors to your site. Unfortunately, spammers can take advantage of these programs.

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.