Bulk Sender Guidelines

Niko Marinis

Oct 18, 2023

247

This article is helpful if you notice your emails going to Gmail accounts are directly going into your recipient's spam folder.

Unfortunately, the IT department can only control the flow of incoming emails, not outgoing emails. Google has strict guidelines on how to ensure your messages reach your intended recipients, and aren't marked as spam.

Below are the following guidelines provided by Google (you can view the direct website here):

Sender Guidelines:

Follow these guidelines to help ensure messages are delivered to Gmail accounts as expected, and to help prevent Gmail from limiting sending rates, blocking messages, or marking messages as spam.

Table of contents:

..............Requirements for all senders

..............Requirements for sending 5,000 or more messages per day

..............Email authentication requirements and recommendations

..............Subscriptions

..............Message Formatting

..............Sending Guidelines

..............Special Considerations

Requirements for all senders:

Starting February 1, 2024, all senders who send email to Gmail accounts must meet the requirements in this section.

Important: If you send more than 5,000 messages per day to Gmail accounts, follow the Requirements for sending 5,000 or more messages per day.

Set up SPF or DKIM email authentication for your domain.
Ensure that sending domains or IPs have valid forward and reverse DNS records, also referred to as PTR records. Learn more
Keep spam rates reported in Postmaster Tools below 0.3%. Learn more
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.
If you regularly forward email, including using 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 senders should also add a List-id: header, which specifies the mailing list, to outgoing messages.

Requirements for sending 5,000 or more messages per day:

Starting February 1, 2024, senders who send more than 5,000 messages per day to Gmail accounts must meet the requirements in this section.

Set up SPF and DKIM email authentication for your domain.
Ensure that sending domains or IPs have valid forward and reverse DNS records, also referred to as PTR records. Learn more
Keep spam rates reported in Postmaster Tools below 0.3%. Learn more
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.
If you regularly forward email, including using 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 senders should also add a List-id: header, which specifies the mailing list, to outgoing messages.
Set up DMARC email authentication for your sending domain. Your DMARC enforcement policy can be set to none. Learn more
For direct mail, the domain in the sender's From: header must be aligned with either the SPF domain or the DKIM domain. This is required to pass DMARC alignment.
For subscribed messages, enable one-click unsubscribe and include a clearly visible unsubscribe link in the message body. Learn more

If you send more than 5,000 emails per day before February 1, 2024, follow the guidelines in this article as soon as possible. Meeting the sender requirements before the deadline may improve your email delivery. If you don’t meet the requirements described in this article, your email might not be delivered as expected, or might be marked as spam. To get help with email delivery issues, go to Troubleshooting.

To learn more about setting up SPF, DKIM, and DMARC, visit Prevent spam, spoofing & phishing with Gmail authentication.

Email Authentification Requirements & Recommendations:

We require that you set up these email authentication methods for your domain. Authenticated messages:

Help protect recipients from malicious messages, such as spoofing and phishing messages.
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 provider. In addition to following the instructions we provide, you should also refer to your domain provider's email authentication instructions.

To verify messages are authenticated, Google performs checks on messages sent 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 in Sender Guidelines. Messages that aren’t authenticated with these methods might be marked as spam or rejected with a 5.7.26 error.

If you use an email service provider, verify that they authenticate your domain’s email with SPF and DKIM.

We recommend you always use the same domain for email authentication and hosting your public website.

SPF

SPF prevents spammers from sending unauthorized messages that appear to be from your domain. Set up SPF by publishing an SPF record at your domain. The SPF record for your domain should reference all email senders for your domain. If third-party senders aren't included in your SPF record, messages from these senders are more likely to be marked as spam. Learn how to define your SPF record and add it to your domain.

DKIM

Turn on DKIM for the domain that sends your email. Receiving servers use DKIM to verify that the domain owner actually sent the message. Learn how to turn on DKIM for your domain.

Important: Sending to personal Gmail accounts requires a DKIM key of 1024 bits or longer. For security reasons, we recommend using a 2048-bit key if your domain provider supports this. Learn more about DKIM key length.

DMARC

DMARC lets you tell receiving servers what to do with messages from your domain that don’t pass SPF or DKIM. Set up DMARC by publishing a DMARC record for your domain. To pass DMARC authentication, messages must be authenticated by SPF and/or DKIM. The authenticating domain must be the same domain that's in the message From: header. Learn how to add a DMARC record at your domain.

We recommend you set up DMARC reports so you can monitor email sent from your domain, or appears to have been sent from your domain. DMARC reports help you identify senders that may be impersonating your domain. Learn more about DMARC reports.

When you set up DMARC, you can then optionally set up BIMI to add your brand logo to messages sent from your domain. Learn how to add your brand logo with BIMI.

ARC

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.

We recommend that senders use ARC authentication, especially if they forward email regularly. Learn more about ARC authentication.

Infrastructure configuration

IP addresses

Your sending IP address must have a PTR record. PTR records verify that the sending hostname is associated with the sending IP address. Every IP address must map to a hostname in the PTR record. The hostname specified in the PTR record must have a forward DNS that refers to the sending IP address.

Set up valid reverse DNS records of your sending server IP addresses that point to your domain. Check for a PTR record with the Google Admin Toolbox Dig tool.

Important: The sending IP address must match the IP address of the hostname specified in the Pointer (PTR) record.

Shared IP addresses

A shared IP address (shared IP) is an IP address used by more than one email sender. The activity of any senders using a shared IP address affects the reputation of all senders for that shared IP.

A negative reputation can impact your delivery rate.

If you use a shared IP 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 Tools to monitor the reputation of the shared IP address.

Subscriptions:

Only send email to people who want to get messages from you so they’re less likely to report messages from your domain as spam.

If messages from your domain are frequently reported as spam, future messages from you are more likely to be marked as spam. Over time, spam reports can lower your domain’s reputation. You can monitor your domain’s reputation with Postmaster Tools.

Make it easy to subscribe

To help ensure your recipients are engaged:

Make sure recipients opt in to get messages from you.
Confirm each recipient's email address before subscribing them.
Periodically send messages to confirm that recipients want to stay subscribed.
Consider unsubscribing recipients who don’t open or read your messages.

Make it easy to unsubscribe

Always give your 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.

To set up one-click unsubscribe, include both of these headers in outgoing messages:

List-Unsubscribe-Post: List-Unsubscribe=One-Click
List-Unsubscribe: <https://solarmora.com/unsubscribe/example>

When a recipient unsubscribes using one-click, you receive this POST request:

"POST /unsubscribe/example HTTP/1.1 Host: solarmora.com Content-Type: application/x-www-form-urlencoded Content-Length: 26 List-Unsubscribe=One-Click"

Learn more about List-Unsubscribe: headers in RFC 2369 and RFC 8058.

Other recommended unsubscribe methods to include when sending email:

Let recipients review the individual mailing lists they’re subscribed to. Let them unsubscribe from lists individually, or all lists at once.
Automatically unsubscribe recipients who have multiple bounced messages.

Message formatting:

Follow these message formatting guidelines to increase the likelihood that Gmail delivers your messages to the inbox instead of the spam folder:

Format messages according to the Internet Format Standard (RFC 5322).
If your messages are in HTML, format them according to HTML standards.
Don’t use HTML and CSS to hide content in your messages. Hiding content might cause messages to be marked as spam.
Message From: headers should include only one email address. For example:
From: [email protected]
Make sure every message includes a valid Message-ID (RFC 5322).
Make sure single-instance message headers are included only once in a message. Examples of single-instance headers include From, To, Subject, and Date (RFC 5322).
Avoid excessively large message headers. To learn more, visit Gmail message header limits.
Web links in the message body should be visible and easy to understand. Recipients should know what to expect when they click a link.
Sender information should be clear and visible.
Message subjects should be accurate and not misleading.
Format these international domains according to the Highly Restrictive guidelines in section 5.2 of Unicode Technical Standard #39:
- Authenticating domain
- Envelope from domain
- Payload domain
- Reply-to domain
- Sender domain

Sending Guidelines:

To reduce the chances that messages from your domain are sent to spam or blocked by Gmail, follow these general best practices:

Recommended sending practices

Authenticate email with SPF and DKIM that are aligned. If you use an email provider, verify that your provider supports this.
Ideally, send all messages from the same IP address. If you must send from multiple IP addresses, use a different IP address for each type of message. For example, use one IP address for sending account notifications and a different IP address for sending promotional messages.
Messages of the same category should have the same From: email address. For example, messages from a domain called solarmora.com might have From: addresses like:
- Sales receipt messages: [email protected]
- Promotional messages: [email protected]
- Account notification messages: [email protected]
Messages sent from an address in the recipient’s contacts are less likely to be marked as spam.

Sending practices to avoid

Don't mix different types of content in the same message. For example, don't include promotions in sales receipt messages.
Don't impersonate other domains or senders without permission. This practice is called spoofing, and Gmail may mark these messages as spam.
Don't mark internal messages as spam. This can negatively affect your domain's reputation, and future messages might be marked as spam.
Don't purchase email addresses from other companies.
Don't send messages to people who didn't sign up to get messages from you. These recipients might mark your messages as spam, and future messages to these recipients will be marked as spam.
Avoid opt-in forms that are checked by default and that automatically subscribe users. Some countries and regions restrict automatic opt-in. Before you opt-in users automatically, check the laws in your region.

Some legitimate messages may be marked as spam. Recipients can mark valid messages as not spam, so future messages from the sender should be delivered to their inbox.

Increase sending volume slowly

When increasing sending volume, keep in mind:

Increasing the sending volume too quickly can result in delivery problems. As you gradually increase your sending mail volume, use Postmaster Tools to monitor mail performance.
For work and school accounts, sending limits apply even when recipients are in different Google Workspace domains. For example, you might send email to users with email addresses that have the domains your-company.net and solarmora.com. Although the domains are different, if both domains have google.com as their MX record, messages sent to these domains count toward your limit.
If you use Google Workspace or Gmail for sending: When you reach the sending limit, Google Workspace limits the message sending rate for the sending IP address.

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, the 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.
If you change the format of bulk emails, increase the traffic segment with the new format gradually.
When making significant changes to sending infrastructure or email or email header structure, increase the modified segment of traffic separately.
If messages start bouncing or start being deferred, reduce the sending volume until the SMTP error rate decreases. Then, increase slowly again. If bounces and deferrals continue at a low volume, review individual messages to identify problems. For example, you can try sending a blank test message and see if it experiences issues.
Stay within the IP limits for sending:
- Be aware of email sending limits when sending from domains that have a Google.com MX host.
- Limit sending email from a single IP address based on the MX record domain, not the domain in the recipient email address.
- Monitor responses so you can change sending rates as needed to stay within these limits.

These factors affect how quickly you can increase sending volume:

Amount of email sent: The more email that you send, the more slowly you should increase sending volume.
Frequency of sending email: You can increase the sending volume more quickly when you send daily instead of weekly.
Recipient feedback about your messages: Make sure you send only to people who subscribe to your emails, and give recipients an option to unsubscribe.

In the event of a recent spike in email activity, adhering to best practices outlined above will likely resolve any deliverability issues automatically during subsequent sends.

Special Considerations:

Using email service providers

Google and Gmail don’t accept allowlist requests from email providers. We can't guarantee messages sent by email providers will pass Gmail’s spam filters.

If you use a third-party email provider to send email for your domain:

Verify that the provider follows the guidelines in this article. Large providers, such as Google, AOL, and Yahoo, typically follow these guidelines.
Make sure the SPF record for your domain includes references to all email senders for your domain. If third-party senders aren't included in your SPF record, messages sent from these providers are more likely to be marked as spam. Learn how to set up your SPF record.

If you use a domain provider but you manage your own email, we recommend you:

Review and follow the best practices in this article for sending email to Gmail accounts.
Use Postmaster Tools to monitor information about messages sent from your domain to Gmail accounts.

Third-party email providers

When clients use your service to send email, you’re responsible for their sending practices. We recommend taking these steps to help manage your clients’ sending activity:

Offer an email address for reporting email abuse, for example: [email protected].
Make sure your contact information in your WHOIS record and on abuse.net are current.
Immediately remove any client who uses your service to send spam.