Article Contents:

• IP warmup plan
  • Path to success
  • What to expect
• Why IP warmup is so important
  • IP warmup helps build a good sender reputation
  • Reputation basics
• Permission and engagement are the key factors
  • Why subscriber engagement matters
  • Remember: quality over quantity
  • How to maintain high customer engagement
• Spam traps
  • Primary spam traps
  • Recycled spam traps
  • How to avoid and remove spam traps

What is IP warmup

IP warmup is the process of gradually increasing the volume of messaging campaign sent from a new IP address. This is done to build a positive sender reputation with email service providers (such as yahoo.com, gmail.com, etc.).

Internet service providers treat email sent from a new IP address as suspicious until a positive sender reputation is established. Achieving maximum email deliverability typically takes 4 to 8 weeks, depending on factors like list targeting, volume, and subscriber engagement.

The IP warmup process may take longer if recipients do not perceive the emails as a mailing they have explicitly signed up for ("opt-in"). Some internet providers limit new senders by imposing volume caps until a positive reputation is established. For example, AOL sets a daily limit of up to 5,000 messages for new senders, while Outlook allows up to 20,000 messages during the first week.

To make a good impression on internet providers from the start, we recommend sending emails only with highly relevant content for recipients.

Focus your initial warmup on your most active subscribers. As you ramp up the volume, gradually incorporate older customer segments into the mailing list. These older segments should be added in small increments — around 10–25% at a time — to avoid damaging your reputation. Run re-engagement or win-back campaigns to reactivate subscribers who signed up more than six months or a year ago (depending on the mailing frequency). Always use fresh email content to increase the chances to recapture customer interest.

The goal of the warmup process is to send emails only to subscribers who are least likely to mark messages as spam or unsubscribe. This typically includes your newest subscribers and those who consistently open your emails or click on links.

The more consistently you maintain the volume, frequency, complaints and unsubscribe rates during the warmup phase, the faster you will build a positive sender reputation.

If you send emails infrequently (less than once a week), it will take more time to establish a positive sender reputation.

IP warmup plan

Path to success

What to expect

Once you begin warming your IP addresses, you may experience some increase in volume and potential blocking. It is important to stick to the plan. Below is detailed information on what to expect and how to respond.

• Mass mailing to Yahoo, AOL, Gmail. Generally, after several mailing cycles with positive metrics, deliverability usually improves, but it may take time to achieve inbox placement for initial messages. The key is to keep sending.

• Potential blocking by internet service providers may occur if your subscriber list lacks sufficient engagement or if you exceed the daily sending limits for each provider, as outlined in the table above. The key is careful list segmentation and potentially reducing your current sending volume to the volume permitted for that week. You can then begin to ramp up volumes according to the specific provider's tolerance. It is important to maintain consistent sending activity.

• It is essential to closely monitor your metrics and adjust your warmup plan accordingly throughout this period.

Why IP warmup is so important

IP warmup helps build a good sender reputation

Sender reputation reflects how recipients perceive you and your emails.

Email reputation directly impacts deliverability:

• Poor reputation => Spam folder or Block;
• Good reputation => Inbox folder.

The reputation of a sender's domain and/or IP address depends on:

• Spam complaints;
• Invalid email addresses (hard bounces);
• Spam trap hits;
• Authentication (SPF, Sender ID, DKIM, DMARC);
• Third-party blacklists;
• Engagement.

Reputation basics

• Subscribers (opt-ins) are the most important.
• If people don’t want your emails, your reputation suffers.
• Recipient behavior and engagement metrics are decisive factors for inbox delivery.
• You cannot transfer your reputation from a previously used IP address.
• If you use the same domain, you may transfer domain reputation. However, providers like Gmail consider both domain and IP reputation, so you should still follow the warmup process.
• Internet service providers trust their users' behavior and observed metrics, so no brand receives preferential treatment.
• B2B senders should follow the same warmup process as B2C senders, as many business domains are now hosted on Yahoo, Outlook, Gmail, AOL, etc.

Permission and engagement are the key factors

Permission is the cornerstone of building a good sender reputation.

Subscribers complain about emails they didn’t expect:

• Are you sending more messages than promised?
• Did they sign up for exactly what they are receiving?
• Does the content you send differ from what you promised?

Why subscriber engagement matters

Internet service providers monitor how engaged your subscribers are with your emails and the nature of that engagement.

Positive actions include:

• Opening the message;
• Adding the email address to the contact list;
• Clicking on links;
• Enabling images;
• Reading speed (e.g., scrolling through the message).

Negative actions include:

• Marking your email as spam;
• Deleting your email;
• Moving it to the junk folder or ignoring it.

Engagement score is another reason to use only opt-in or confirmed opt-in email marketing lists. Permission-based lists maximize engagement likelihood, as the recipient already has an established relationship with the sender, at least in theory.

Remember: quality over quantity

• You pay based on your mailing volume. If a message is never opened, that money is wasted.
• Return on investment (ROI) decreases when passive subscribers are included in campaigns.
• Inactive subscribers often cause spam complaints, spam trap hits, and hard bounces, which can harm deliverability for active subscribers and reduce ROI.
• Run regular re-engagement campaigns to reactivate inactive subscribers.
• Send messages to inactive subscribers less frequently than to active ones.

How to maintain high customer engagement

• Send relevant content to active subscribers.
• Set clear expectations from the start.
• Allow subscribers to choose their preferred email frequency (e.g., daily, weekly digest, or triggered by product availability). If you send infrequently, explain why. Ask subscribers to add you to their address book upon sign-up.
• Implement an onboarding program to set expectations.
• Keep your mailing lists clean — remove invalid email addresses and spam traps.
• Start by cleaning your registration forms. If possible, block spammy, personal, or role-based email addresses.
• As your lists age, filter out inactive subscribers.

Spam traps

Primary spam traps

Email addresses created solely to catch spammers. These email addresses have never belonged to real people, never subscribed to mailing programs, and never made any purchases. If your emails hit these pristine traps, it usually indicates you have a poor data collection partner.

Recycled spam traps

Email addresses that once belonged to real users but were abandoned and later repurposed by internet providers as spam traps. Before converting a dormant address into a spam trap, providers typically return a "user unknown" error for a certain period (6 to 12 months). If your emails hit a recycled spam trap, it usually means your data hygiene process is ineffective.

How to avoid and remove spam traps

• Never buy or rent mailing lists;
• Remove hard bounces;
• Regularly run re-engagement campaigns for inactive subscribers;
• Remove inactive subscribers after multiple failed attempts to re-engage them.