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How to warm up an IP address

Mailbox providers are cautious about the email activity from new IP addresses. Spammers frequently set up new IPs and immediately start sending large volumes of email.

It’s important to warm up your IPs so you can build a good sending reputation and improve your chances of getting your email into your subscribers’ inboxes. There’s no guarantee that you will not have some deliverability challenges at first, but using these best practices will help set you up for long-term success.

Successfully warming up your IP address involves completing the pre-warming checklist and creating an effective warming schedule based on your email program and sending reputation. It requires careful and deliberate monitoring of your performance, and potentially adjusting your daily sending volumes as needed based on that performance.

To help minimize the potential disruption to your business, it is highly recommended that you contact your ESP or Return Path account representative for guidance prior to starting the warm up.

What to expect

  • During the first week you will have some deliverability problems while the new IP is building a sending reputation. Depending on the quality of your subscribers and your email marketing practices , you may see additional deliverability issues continue during the warmup process.
  • If your sending practices and reputation are poor prior to the warmup, a new IP address won't help you increase your inbox placement in most cases.
    • If you historically achieve 70% inbox placement at most mailbox providers and you don't change your practices, it's likely that your inbox placement will eventually end up at the same rate once the warmup process is completed.
    • You may also see your inbox placement decrease due to the lack of sending history on the new IP.
  • Some mailbox providers will deliver a portion of your email to the spam or junk folder to see if subscribers rescue it and label it as 'not spam'. Subscribers labeling your email as 'not spam' is a positive indicator used by mailbox providers to see you as a legitimate sender, so sending engaging email to people that want it is important.
  • The warming up process will probably take about 30 days. It might take longer (or shorter) depending on:
    • The volume of email you send
    • The quality of your subscriber list
    • How frequently you send
  • If you send email daily, your warm up will go faster than if you send weekly.
  • If you rush your warm up or do not plan and manage it carefully, there’s a good chance you will have problems getting your email delivered to the inbox for a while.
  • AOL, Outlook.com and Gmail usually need a longer warm-up period.

Pre-warming checklist

Before warming up your IP address:

  • Make sure the IP has a pointer (PTR) record set up in your reverse Domain Name System (DNS).
  • Sign up the IP with all available mailbox provider complaint feedback loops.
  • Add the IP address to a Microsoft Smart Network Data Services (SNDS) account so you can monitor the reputation data the service provides.
  • Add the List-Unsubscribe header to your email headers. The List-Unsubscribe header is an optional header that you can include in your email messages which is designed to help reduce complaints by providing subscribers an alternative method to safely unsubscribe without negatively impacting your sending reputation.
  • Confirm that all email you send from the new IP is authenticated with DomainKeys Identified Mail (DKIM).
  • Update your Sender Policy Framework (SPF) record with the new IP.
  • Check the IP to make sure it is not set up as an open relay. Ask your Email Service Provider (ESP) or email administrator to confirm this.
  • Make sure your bounce processing is set up and tested, and that unknown users are removed after one bounce.
  • If you are a member of Return Path Certification:
    • Ask to have the new IP added to your account.
    • Make sure to let the Certification team know that it is a new IP and give them your timeframe for warming it up.
  • Add the new IP to Reputation Monitor.
  • Confirm that you are sending to the seed list from this IP.
  • Identify your engaged subscribers, which are those who open, click, and buy, in the following buckets:
    • Less than 30 days
    • 30-60 days
    • 60-90 days
    • 90-180 days
    • Over 180 days  
  • Clean up your list by removing malformed domains, unknown users, and unengaged subscribers.

If you are also changing domains:

  • If you are using a new d= domain in the DKIM signature, add the new domain to the Yahoo! complaint feedback loop.
  • Create a new SPF record, if applicable.
  • Update the Whois record for each domain with the correct information. Do not use a domain privacy service.
  • Create an [email protected] and [email protected] role account for each domain and ensure they are monitored.
  • Add the [email protected] and [email protected] role accounts to abuse.net for each domain.
  • Create a Domain-based Message Authentication, Reporting and Conformance (DMARC) record for each new domain and set the policy to monitor (p=none).

Warming up an IP address

Use these general guidelines to ensure your IP warming goes as smoothly as possible. The best way to start is to create a warm-up schedule based on your own sending practices and business needs.  

  • Send email from the new IP to the Return Path Seed List throughout the warm-up period. You can use Inbox Monitor to see the progress of your warm up and make any adjustments needed to improve inbox placement. You may need to adjust your daily sending volumes, or your connection and throughput settings.
  • Start with a low sending volume of 5,000 total subscribers across all mailbox providers.
  • Send to your most engaged subscribers first and gradually introduce other segments of your list with less engaged subscribers.
  • Double your sending volume every three to four days until you reach your maximum daily volume.
  • Don't force through volume just to hit the volume threshold for that day. For example, if you are sending to 10,000 subscribers on day five, but your only send volume for that day is for 8,500 subscribers, don't bother coming up with another 1,500 subscribers to make up the difference. Allow for natural daily fluctuations and just cap the volume for the day.
  • Monitor your bounce logs, Inbox Monitor, and Reputation Monitor for deliverability problems. Mailbox providers have different tolerances for increasing volume on a new IP.
  • Apply for AOL whitelisting after sending consistent volumes for two to four weeks from the new IP. Before you apply to the whitelist, ensure that your new IP has a good reputation at AOL by using AOL's IP reputation check. Whitelisting does not guarantee inbox placement but you should see your deliverability improve after you are accepted.
  • After four weeks of consistent sending volume from the new IP, notify Yahoo! that you are sending from a new IP. You do this using its new Sender Application form. This is not a whitelist, but Yahoo! may make adjustments to its filters that can improve deliverability if your new IP has a good sending reputation. Notifying Yahoo! about your new IP does not guarantee inbox placement.

If deliverability problems occur:

  • Pause sending or reduce volumes to allow spam filters to adjust to the new IPs.
  • Stop sending to mailbox providers where policy blocks occur; then troubleshoot and fix the cause. Resume sending only after the issue has been fixed.
    • For AOL issues, pause sending for at least one hour and try to identify and fix the cause. Resume sending slowly and monitor closely for additional problems.
  • Make sure your complaint processing and bounce processes are working correctly.
  • Check to see if you accidentally sent to:
    • A suppression list
    • The entire list file
    • A large number of unengaged subscribers

If you did, hold your volumes at the current level for a few days, then start back up on the original warmup plan, and make sure to send to engaged subscribers right away.

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