How to warm up a SMTP IP address?

What is IP Warm-up?
IP warming is the practice of progressively increasing email volume to a new IP address over a period of days or weeks to create a good sending reputation with mailbox providers.

Warm-up for IP Summary
Email from a new IP address is seen as suspect by mailbox providers unless it has a positive sending reputation. Maximum deliverability takes 4-8 weeks to attain (depending on targeted volume and engagement). If mailbox providers do not believe that the email is “desired” by the receiver, warming may take longer (i.e., the recipient has signed up explicitly). Until a sender establishes a reputation, certain mailbox providers limit them to thresholds — the number of messages delivered every day.

Warm-up your most engaged subscribers first, and then gradually add in older groups as you proceed. To avoid tipping your reputation from excellent to poor, older segments should be introduced to engaged segments in chunks of 15% of your present traffic. During the warm-up period, your aim is to email to subscribers who are least likely to complain or bounce. This would include individuals who have lately opted in and are consistent openers/clickers.
The more consistent you are with volume, frequency, complaint, and bounce levels throughout the Warm-up period, the faster you will develop a favorable sending reputation. If you transmit seldom – less than weekly – it will take longer to grow.

Key to Success

  • During weeks 1-2 send to your most active subscribers – those who have opened/clicked in the past 30 days
  • During weeks 3-4, you can expand to subscribers who have opened/clicked in the past 60 days
  • During the first 6 weeks do NOT send to subscribers who have not opened or clicked in the past 90 days
  • If warming above 10 million subscribers, consider adding another IP
Week 1 Daily Volume per IP
Day 1 200
Day 2 500
Day 3 1,000
Day 4 2,000
Day 5 5,000
Day 6 10,000
Day 7 20,000
Week 2
Day 8 40,000
Day 9 50,000
Day 10 75,000
Day 11 100,000
Day 12 150,000
Day 13 200,000
Day 14 250,000
Week 3
Day 15 325,000
Day 16 400,000
Day 17 500,000
Day 18 600,000
Day 19 750,000
Day 20 1,000,000
Day 21 1,250,000
Week 4
Day 22 1,750,000
Day 23 2,000,000
Day 24 3,000,000
Day 25 4,250,000
Day 26 5,000,000
Day 27 6,000,000
Day 28 7,500,000
Final Week
Day 29 10,000,000
Day 30 DONE

What You Can Expect

  • When you start warming up your IPs, you may expect some bulking and blocking. It is critical to keep to the strategy. Details on what to expect and measures to take are provided below.
  • Bulk emailing at Yahoo, AOL, and Gmail. It usually clears up after a few emails with good positive metrics, although inbox delivery can take some time. The idea is to continue emailing active subscribers.
  • AOL, Microsoft, and Comcast all experienced delays. The delays (421 bounces) will retry for 72 hours and will bounce as a 5XX with the original 421 faults in the bounce record if not delivered. Delays are to be expected, and they will become less frequent as the company’s reputation grows. There is no need to be concerned as long as they provide. If they are time out in significant numbers, you should reduce your volumes to that mailbox provider by narrowing your interaction window.
    If the list is not sufficiently engaged, mailbox providers may block it. The idea is to precisely segment and tightens interaction. The trick, once again, is to keep sending.

Why is IP Warm-up Important?
Warm-up Matters

Quick Warm-Up: Slow Warm-Up:
  • Mailbox providers see volume spikes
  • Unknown Senders
  • Blocks/Filtering/Rate Limiting will occur
  • Mailbox providers see the gradual build in volume
  • Good reputation develops over time
  • Blocks/Filtering/Rate Limiting rarely occurs (only occurs when engagement and complaint rates are low).

IP Warm-up Helps Build Your Sender Reputation

Sender Reputation is how mailbox providers view you and your mail.

  • Email reputation controls access to the inbox
    • Bad reputation = Spam Folder or Blocks
    • Good reputation = Inbox
  • Reputation can affect the domain and/or IP address and will be based on:
    • Spam complaints
    • Invalid email addresses (hard bounces)
    • Spam trap hits
    • Authentication (SPF, DKIM, DMARC)
    • Third-party blacklistings
    • Engagement

Positive effects on your reputation are:

  • Opens
  • Clicks
  • Authentication – DKIM, SPF, DMARC

Negative effects on your reputation are:

  • Poor or insufficient permission
    • High recipient complaints (report as spam)
  • Poor list quality/hygiene – bad email addresses
  • IP address and domain blacklistings
  • Spam trap hits
  • Large spikes in volume
  • The Fundamentals of Reputation

Key Takeaways:

  • Opt-ins are most important
  • If people do not want your mail, your reputation suffers
  • Mailbox providers and metrics are judge and jury when it comes to getting delivered to the inbox.
  • You can not transfer your reputation from your previously used IP.
  • If you use the same domain that reputation can follow you, however, mailbox providers like Gmail use the reputation of the domain coupled with the reputation of the IP therefore you must follow the warm-up process.
  • Mailbox providers trust metrics from their users and what they observe, therefore, no brand will get special treatment.
  • B2B senders must follow the same warm-up process as B2C senders as many business domains are now hosted by Yahoo, Outlook, Gmail, AOL, etc.

Permission and Engagement is Key
Permission is the cornerstone of building a good sender reputation.

  • Subscribers complain about mail they are not expecting to receive.
    • Are you sending more frequently than you said you would?
    • Did they sign up for exactly what they are receiving?
    • Are you sending content other than what you said you would?
  • Are you following best practices by staying up on the Can-Spam Act and the CASL laws?

Why is Engagement Important?

Mailbox providers track how engaged subscribers are with an email and its sender, and the nature of the engagement.

  • Positive actions may include opening a message, adding an email address to the contact list, clicking through links, clicking to enable images, and read rates such as scrolling through the message.
  • Negative actions may include reporting the email as spam, deleting it, moving it to the junk folder, or ignoring it.
  • Engagement ratings are another compelling reason to use only opt-in or confirmed opt-in email marketing lists. Opt-in maximizes the likelihood of engagement because in theory there is a relationship already established with the mailbox provider.

Remember Quality Always Wins Out Over Quantity.

  • There is a charge for the volume you send. If the message is never opened that cost is wasted.
  • Lower ROI when including disengaged subscribers in your campaigns.
  • Disengaged subscribers are the common cause of complaints, spam traps, hard bounces which can affect deliverability/inbox placement to engaged subscribers which lowers your ROI.
  • Run regular re-engagement campaigns to win back the disengaged subscribers.
  • Send to the disengaged subscribers less frequently than engaged subscribers.

How to Keep your List Highly Engaged

  • Send relevant content to engaged subscribers.
  • Set subscribers’ expectations from the beginning.
  • Give people who opt-in to your mail choices on how often they’ll receive emails from you (e.g., once daily, a weekly digest, as items become available or go on sale). If you send infrequently, make that clear. Ask them to whitelist you as they were opt-in.
  • Deploy a good onboarding program educating them on expectations.
  • Keep your lists clean.
  • Begin with your registration forms. If you have the option to block spammy, personal, or role-based email addresses, do so.
  • As the age of your list, weed out nonengaged subscribers.

Spam Traps

  • Pristine Spam Traps: Email addresses created solely to capture spammers (sometimes referred to as “Honey Pots”). These email addresses were never owned by a real person, do not subscribe to email programs, and of course will never make a purchase. If you are hitting pristine traps, this typically indicates you have a bad data partner and/or poor list acquisition practices.
  • Recycled Spam Traps: Email addresses that were once used by a real person but abandoned and then recycled by mailbox providers as spam traps. Before turning an abandoned email address into a spam trap, mailbox providers will return an unknown user error code for a period of time (6 to 12 months). If you are hitting a recycled spam trap, this typically indicates that your data hygiene process is not working.

How to Avoid and Remove Spam Traps

  • Do not purchase or rent lists.
  • Remove hard bounces.
  • Continuously re-engage your inactive subscribers.
  • Remove unengaged subscribers (if re-engagement attempt is not successful).