Summary
Failing to properly warm up an IP address before sending email campaigns results in severe deliverability issues and a damaged sender reputation. Email providers view a sudden surge in email volume from a new IP address as suspicious, often flagging it as spam. This can lead to emails being filtered into the spam folder, blocked entirely, or the IP address being added to blocklists. A gradual warm-up is crucial to establish trust with ISPs and ensure emails reach the intended recipients. Real-world examples highlight instances where rapid warm-ups led to months of spam classification, underscoring the importance of following best practices.
Key findings
- Deliverability Impact: Poor IP warming leads to emails landing in spam folders or being blocked by ISPs.
- Damaged Sender Reputation: Inadequate warm-up damages sender reputation, impacting future deliverability.
- ISP Suspicion: ISPs view sudden spikes in email volume from new IPs as suspicious activity.
- Potential Blacklisting: Failure to warm up properly can result in the IP address being added to blocklists.
- Examples of Failures: Rapid warm-ups can lead to prolonged periods of spam classification.
Key considerations
- Gradual Increase: Implement a gradual IP warm-up process to build sender reputation over time.
- Monitor Deliverability: Closely monitor deliverability metrics during and after the warm-up process.
- Segmentation: Consider segmenting by ISP to tailor the warm-up process to specific providers.
- Recognize Risks: Be aware of the risks associated with sending from a new IP and take precautions.
- Establish Legitimacy: Implement legitimate sending practices to avoid being marked as a spammer.
What email marketers say
8 marketer opinions
Failing to warm up an IP address correctly results in significant deliverability issues. Email providers view sudden spikes in email volume from a new IP as suspicious, often flagging the sender as a spammer. This leads to a damaged sender reputation, with emails being filtered to spam folders, blocked entirely, or even causing the IP to be blacklisted by ISPs. Proper IP warming establishes trust with ISPs and ensures emails reach the intended recipients.
Key opinions
- Deliverability impact: Poor IP warming directly impacts deliverability, with emails ending up in spam or being blocked.
- Sender reputation damage: Inadequate warm-up damages sender reputation, making it harder to reach inboxes in the future.
- ISPs suspicion: ISPs flag sudden email volume increases from new IPs as suspicious activity.
- Real-world examples: Examples exist of rapid warm-ups leading to months of spam classification by major providers.
Key considerations
- Gradual increase: Implement a gradual IP warm-up process to build sender reputation over time.
- Monitor deliverability: Closely monitor deliverability metrics during and after the warm-up process.
- Segment by ISP: Consider segmenting sending by ISP to tailor the warm-up process to specific providers.
- New IP risks: Recognize the risks associated with sending from a new IP and take precautions.
Marketer view
Marketer from Email Geeks shares an example of a client who warmed up too fast (1k-2k one day then 100k the next day) and were marked as spam at Yahoo for months.
7 Jun 2025 - Email Geeks
Marketer view
Email marketer from StackExchange explains that ISPs use algorithms to detect spammers. A sudden spike in traffic from a new IP looks suspicious, so ISPs will filter the mail as spam until the server builds up a good reputation.
20 Feb 2023 - StackExchange
What the experts say
2 expert opinions
Experts agree that failing to warm up an IP address correctly can lead to severe deliverability problems. Sending large volumes of email from a new, unwarmed IP triggers suspicion from ISPs and inbox providers. This heightened scrutiny increases the likelihood of being flagged as a spammer, resulting in email placement in the spam folder, message blocking, and potential blacklisting.
Key opinions
- Risk of being tagged as a spammer: ISPs flag new IPs sending high volumes as potential spammers.
- Deliverability issues: Lack of warm-up leads to emails being marked as spam or blocked.
- Potential blacklisting: Poor warm-up practices can result in blacklisting of the IP.
- ISP Suspicion: Sending too much volume from an IP without warming can result in inbox providers treating your mail with suspicion
Key considerations
- Implement IP warm-up: Always implement a proper IP warm-up strategy for new IPs.
- Gradual ramp-up: Increase sending volume gradually to build a positive reputation.
- Monitor deliverability: Track deliverability metrics and address any issues promptly.
Expert view
Expert from Word to the Wise shares that sending too much volume without warming an IP can result in inbox providers treating your mail with suspicion. This can lead to placement in the spam folder, or even complete blocking of your messages.
4 Mar 2022 - Word to the Wise
Expert view
Expert from Spam Resource explains that if you don't warm up your IP address, you run the risk of being tagged as a spammer. ISPs see a new IP sending a huge volume of email as a red flag, leading to deliverability issues and potential blacklisting.
15 Oct 2024 - Spam Resource
What the documentation says
4 technical articles
Documentation from multiple sources indicates that failing to properly warm up an IP address results in significant deliverability issues and damage to sender reputation. Major email providers like Gmail and Outlook.com will filter or block emails from new IPs sending high volumes of mail without a gradual warm-up. This behavior can lead to the IP being listed on blocklists due to perceived spam activity, further hindering deliverability.
Key findings
- Negative impact on IP reputation: Sudden spikes in email volume from new IPs without warm-up negatively impact IP reputation with Gmail.
- Deliverability issues with Outlook.com: Inadequate IP warming leads to deliverability problems with Outlook.com; emails may be flagged as spam.
- Risk of blocklisting: Sending high volumes of unsolicited email from a new IP can cause it to be listed on blocklists.
- Damage to sender reputation: Not warming up an IP correctly damages sender reputation and deliverability.
Key considerations
- Gradual volume increase: Gradually increase email volume when sending from a new IP to establish a positive sending reputation.
- Avoid unsolicited email: Refrain from sending high volumes of unsolicited email from new IPs to prevent blocklisting.
- Monitor sender reputation: Monitor sender reputation to ensure emails are not being filtered as spam.
- Establish legitimate practices: Verify and implement legitimate sending practices to avoid being considered a spammer by email providers.
Technical article
Documentation from RFC Editor explains that sending a high volume of unsolicited email from a new IP address can cause it to be listed on various blocklists, due to perceived spam activity. This makes the email server untrusted.
28 Mar 2024 - RFC-Editor.org
Technical article
Documentation from Microsoft Docs shares that inadequate IP warming can lead to deliverability issues with Outlook.com. Microsoft's filtering systems may flag your emails as spam if you send a large volume of emails from a new IP address without gradually increasing volume and establishing a positive sending reputation.
20 Jun 2024 - Microsoft Docs
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