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5 IP Warm Up Tips That Will Get You To The Inbox

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We’ve talked a lot about why it’s important to warm up your IP, tips on warm up timelines and sending volume, and top questions you should ask your ESP before getting started. At this point, you may be asking yourself…why not just jump in head first and see what happens?

While it may be tempting to fast track your IP warm up process, remember, patience is a virtue. Recovering from a bad move can be more costly than taking the time to build a good reputation. If you keep these 5 tips in mind, you’ll be off to a great start:

1) Starting cautious is good. It’s very hard to repair a bad reputation. Oftentimes, senders need to be more aggressive in order to get their emails out the door. However, you must also consider how much time it may take to fix your reputation. Since sending reputation is tracked every 30 days, it could take 4 or more weeks to rebuild it, and every day you get blocked can cost you.

2) IP rotation is bad business. You don’t need dozens of IPs. If you do, and the ISPs get wind of it, they will block the whole IP range. You can send millions of messages per day from a single IP if you warm up properly and continue to follow best practices.

Need proof? Here’s a true life case of too many IPS…

A daily deal site was being blocked by Hotmail, but was unsure why. Prior to coming to SendGrid, they were sending anywhere from thousands to millions of emails per day off of 17 different IP addresses.

Why? In order to maximize delivery, they would cherry pick the IP with the best reputation and deploy mail through that IP. This process is called snowshoeing and represents bot-net behavior which ISPs red flag. While ISPs use your IP address to determine reputation, they can also see the sending domain. To remedy this problem, SendGrid moved all of their email streams to 2 IPs and developed a customized sending schedule. Their warm up period topped out at 15 days when they reached full volume and maximum delivery. Success!

3) Use the data to educate you. This is a great opportunity to optimize your email program, even if you are experiencing delivery failures. ISPs like to see that you are being responsive. It’s a small community and word gets around, so doing the right thing will always work in your favor.

4) Marketing email is still a challenge. Be more careful and scrupulous with marketing email.  Since transactional email is viewed as “wanted” email in the eyes of the ISPs, it’s generally granted a little more leeway. This is why we recommend getting at least two dedicated IPs—one for marketing email and the other for transactional.

5) Best practices will get you everywhere. Monitoring user engagement, personalization, and ultimately removing inactives while you are warming up your IP and after is key to maximum email deliverability for the life of your email program.

The Bottom Line of IP Warm Up

Warming up your IP is a vital part of creating a healthy email program. With the right tools and information you can ensure your email gets inboxed with each deployment. At SendGrid, we work with customers to provide the best strategies and advice to help make their IP warm up successful. We have detailed reporting by ISP which helps give our customers an inside look at how their email is being received and our 24/7 support team is always on call if you need.

For an extensive overview of the IP warm up process, download our free How To Warm Up and IP guide here.



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Postmaster Tools

If you send a large volume of emails to Gmail users, you can use Postmaster Tools to see: 

  • If users are marking your emails as spam
  • Whether you’re following Gmail's best practices
  • Why your emails might not be delivered
  • If your emails are being sent securely




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Bulk Senders Guidelines

Troubleshoot delivery issues with Postmaster Tools

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
Third-Party Senders
Affiliate Marketing Programs

Not in the right place?

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

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.


Authentication & Identification

Why is it important to authenticate your messages?

Authentication ensures that your messages can be correctly classified. Emails that lack authentication are likely to be rejected or placed in the spam folder, given the high likelihood that they are forged messages used for phishing scams.

In addition, unauthenticated emails with attachments may be outrightly rejected, for security reasons.

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

  • 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.



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

  • Through an email asking to subscribe to your list.
  • By manually checking a box on a web form, or within a piece of software.

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:

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

  • 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.

To make sure recipients can unsubscribe without leaving Gmail, we strongly recommend adding a 'List-Unsubscribe' header in one of the following ways:

  • One-click: Add the following headers as described in RFC 8058:
  •      List-Unsubscribe-Post: List-Unsubscribe=One-Click
         List-Unsubscribe: <https://example.com/unsubscribe/opaquepart>

                If the recipient unsubscribes, you'll get this POST request:

         POST /unsubscribe/opaquepart HTTP/1.1
         Host: example.com
         Content-Type: application/x-www-form-urlencoded
         Content-Length: 26


  • mailto: Provide a List-Unsubscribe header that points to an email address using the 'mailto:' method

Note: If both one-click and mailto methods are present in the List-Unsubscribe header, Gmail will use the method specified first.

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

  • 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.

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

  • 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.



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:

  • 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.

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:

  • Using separate email addresses for each function.
  • Sending mail from different domains and/or IP addresses for each function.

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.  

  • You must have an email address available for users and/or clients to report abuse (abuse@yourdomain.com).
  • 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.


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 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.

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



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