Is an IP warm-up necessary when I switch to a new ESP?

Yes, an IP warm-up is almost always necessary when migrating ESPs, especially if you are getting new dedicated IP addresses. Mailbox providers see new IPs as unknown, and a sudden surge in volume can trigger spam filters. Even with shared IPs, a careful warm-up is advisable to protect your sender reputation.

Should I use a new subdomain or keep my existing one?

It's often recommended to use a new subdomain when migrating ESPs, especially if there will be an overlap in sending from both providers during the transition. A new subdomain provides a fresh reputation slate, preventing potential conflicts or inherited negative reputation from your old sending practices. However, if your current subdomain has an excellent reputation and there's no overlap, reusing it can be an option after updating DNS records.

How long does a typical IP and subdomain warm-up take?

The duration of an IP and subdomain warm-up can vary significantly based on your sending volume, list quality, and audience engagement. It typically ranges from 2 weeks to 2 months. High-volume senders or those with less engaged lists may require a longer warm-up. It's not a fixed timeline but rather a process of building trust, which means you need to monitor your performance and adjust the pace accordingly.

What metrics should I monitor during the warm-up period?

You should closely monitor open rates, click-through rates, bounce rates, and complaint rates. Use your ESP's analytics, Google Postmaster Tools , and blocklist monitoring tools to detect any issues. If you observe declining engagement or increased bounces/complaints, slow down your sending volume and investigate the cause.

Is it beneficial to separate marketing and transactional emails onto different IPs and subdomains?

Yes, separating marketing and transactional email streams onto different subdomains and IP addresses (ideally dedicated) is a best practice. This helps isolate the reputation of each stream. If your marketing emails encounter deliverability issues, your critical transactional emails will remain unaffected, ensuring essential communications reach your users reliably.

What are the best practices for migrating ESPs with subdomain and IP warmups? - Sender reputation - Email deliverability - Knowledge base

Migrating Email Service Providers (ESPs) is a significant undertaking that requires careful planning to maintain your sender reputation and ensure email deliverability. A common misconception is that if you've warmed up your domain and IP with one ESP, you can immediately send high volumes when switching. However, that's rarely the case. When you move to a new ESP, especially if it involves new dedicated IP addresses or a new subdomain, a strategic warm-up process is essential to establish trust with mailbox providers and prevent your emails from landing in the spam folder.

The primary goal during an ESP migration is to transfer your sending volume and reputation seamlessly without triggering spam filters or encountering blocklists (or blacklists). This involves carefully managing your sending infrastructure, especially your subdomains and IP addresses. My experience has shown that a well-executed warm-up minimizes disruptions and protects your email program's effectiveness.

It’s not just about moving data, it’s about preserving your sender's identity and credibility. We need to consider whether to keep the same sending subdomain or establish a new one, how to manage dedicated versus shared IPs, and what a realistic warm-up schedule looks like for different mail streams, such as marketing and transactional emails.

This guide will walk you through the critical best practices for migrating ESPs, focusing on the nuances of subdomain and IP warm-up strategies to ensure your emails continue to reach the inbox effectively.

Planning your ESP migration

Before you even think about hitting send on your new ESP, thorough preparation is crucial. This phase sets the foundation for a smooth migration and successful warm-up. We always emphasize the importance of cleaning your email lists and segmenting your audience.

Start by scrubbing your contact lists to remove unengaged subscribers, bounces, and known spam traps. Sending to a clean, engaged list during warm-up is paramount, as it helps establish a positive sending reputation from the outset. I recommend focusing on your most engaged recipients first, as they are most likely to open and click your emails, signaling positive engagement to mailbox providers. This initial engagement is vital for building trust.

When migrating to a new ESP, one of the first decisions you'll face is whether to use your existing sending subdomain or set up a new one. This choice impacts how mailbox providers perceive your email stream and influences your warm-up strategy. Domain warm-up is always necessary with a new platform, regardless of IP.

Leverage existing reputation: If your current subdomain has a strong, positive sending history, keeping it can provide a slight advantage, as it carries some established trust with ISPs (Internet Service Providers).
Simpler DNS changes: You simply update the CNAME records to point to your new ESP's infrastructure, rather than creating new ones.
Reduced complexity: Less chance of brand confusion for recipients if the sending domain remains consistent.

Using an existing subdomain

If you decide to reuse your existing subdomain, it's vital to ensure a clean break from your old ESP. Remove all CNAME and TXT records that were previously generated by your old provider. This prevents conflicts and ensures your new ESP can properly configure the domain.

Benefit: Potential to carry over some existing domain reputation.
Consideration: If the subdomain has a poor history or is on a blocklist (blacklist), you might inherit negative reputation. You can check its blocklist status with our tool.

Setting up a new subdomain

Establishing a new, clean subdomain is often the safer and more recommended approach, especially if there will be any overlap in sending from both ESPs during the migration. This creates a fresh reputation slate with mailbox providers.

Benefit: A fresh start with no inherited negative reputation.
Consideration: Requires a full domain and IP warm-up. We typically recommend separating marketing and transactional mail onto different subdomains and dedicated IPs.

Regardless of your subdomain choice, your authentication records (SPF, DKIM, DMARC) must be correctly configured for your new ESP. These are foundational for deliverability. I recommend using our DMARC record generator to ensure proper setup. Incorrect records can lead to emails being marked as spam or rejected outright.

Implementing the warmup process

The warm-up process is a gradual increase in sending volume, designed to build trust with ISPs for your new IP addresses and subdomain. This is crucial for maintaining your sender reputation, as a sudden spike in volume from a new IP or subdomain can flag your emails as suspicious.

We start by sending small volumes of email to your most engaged subscribers. As your reputation builds, we gradually increase the volume and broaden the recipient base. The key is consistency and patience. A typical warm-up schedule varies based on your total volume, list quality, and engagement levels. For instance, transactional emails may warm up faster due to higher engagement, while marketing emails require a more cautious approach. It's often recommended to set a consistent sending cadence.

For specific guidance on different warm-up scenarios, you can refer to our articles on dedicated IP warm-up, warming up with shared IPs, and subdomain warm-up processes.

Day	Volume Increment	Target Audience
Days 1-3	500-1,000 emails	Highly engaged subscribers (opened/clicked in last 30 days)
Days 4-7	2,000-5,000 emails	Engaged subscribers (opened/clicked in last 60-90 days)
Days 8-14	5,000-10,000 emails	Moderately engaged subscribers (opened/clicked in last 6 months)
Weeks 3-4	Gradual increase, up to 25% daily volume growth	All active subscribers, progressively including less engaged
After Week 4	Full volume	Entire mailing list

This schedule is a general guideline. Actual warm-up times can vary significantly based on the volume you send, the quality of your list, and your engagement rates. If you encounter any issues, you might need to slow down the warm-up and re-evaluate your sending strategy. Remember, the goal is to build a positive reputation, not to rush the process.

Monitoring and adjusting during warmup

Monitoring your email performance diligently throughout the warm-up period is non-negotiable. This means keeping a close eye on key metrics like open rates, click-through rates, bounce rates, and complaint rates. Anomalies in these metrics can signal that you need to adjust your sending volume or strategy.

Key metrics to monitor

Open rate: A healthy open rate indicates that your emails are reaching the inbox and resonating with recipients. A drop could mean deliverability issues.
Click-through rate (CTR): Similar to open rates, a strong CTR shows engagement and positive reception of your content.
Bounce rate: Keep this as low as possible. High bounce rates signal a problematic list and can negatively impact your sender reputation. Separate hard and soft bounces.
Complaint rate: The most critical metric. High complaint rates (e.g., above 0.1%) can lead to quick blocklisting (blacklisting) and severe deliverability issues. Promptly remove recipients who mark your emails as spam.

Utilize tools like Google Postmaster Tools and your ESP's analytics dashboards for real-time insights into your sending performance. These platforms provide valuable data on delivery errors, spam complaints, and reputation scores, allowing you to react quickly to any negative trends. Monitoring blocklists (blacklists) is also crucial. Regularly check if your new IPs or subdomain have been added to any major blocklists. If you find yourself on a blocklist, investigate the cause immediately and take steps to remedy the situation and request delisting.

Finally, be prepared to adjust your warm-up plan based on the feedback you receive from mailbox providers and your engagement metrics. If you see signs of throttling or increased spam placement, slow down your sending volume and re-engage your most active users. Flexibility and continuous optimization are key to a successful ESP migration and long-term deliverability.

Views from the trenches

Best practices

Always clean your email list before migrating; remove inactive subscribers and spam traps.

Segment your audience and start warming up with your most engaged subscribers first.

Separate marketing emails from transactional emails onto different subdomains and IPs.

Continuously monitor your sender reputation and engagement metrics using analytics tools.

Ensure SPF, DKIM, and DMARC are properly configured for your new sending setup.

Common pitfalls

Sending too much volume too soon from new IPs or subdomains, which can trigger spam filters.

Not cleaning your list before migration, leading to high bounce and complaint rates.

Failing to update DNS records (CNAME, TXT) correctly for your new ESP, causing authentication failures.

Ignoring early warning signs from deliverability metrics like high bounce rates or low open rates.

Attempting to reuse a subdomain with a poor sending history, inheriting its bad reputation.

Expert tips

When doing any overlap in ESPs, it's safer to set up a new subdomain.

IP reputation mainly impacts the SMTP transaction; domain reputation often matters more for delivery.

While dedicated IPs can handle large volumes, monitor performance closely and add more if needed.

Keep the 5321.From domain consistent if possible, it's more crucial than the exact FQDN.

Avoid having your new ESP

Expert view

Expert from Email Geeks says: Preserving the 5321.From domain is more crucial than the exact FQDN, and a smooth cut-over with updated authentication is key.

2020-09-23 - Email Geeks

Expert view

Expert from Email Geeks says: IP reputation is important for the SMTP transaction, but for consumer domains, other factors often play a larger role in final delivery.

2020-09-23 - Email Geeks

Navigating your ESP migration for deliverability

Migrating ESPs with subdomain and IP warm-ups is a complex but manageable process. The core principle is to build and maintain trust with mailbox providers by gradually introducing your new sending infrastructure. This means meticulous planning, careful execution of your warm-up schedule, and continuous monitoring of your email performance. The decision to use an existing or new subdomain, along with the choice of dedicated or shared IPs, heavily influences your strategy.

Prioritizing a clean list and engaged recipients during the initial warm-up phases is critical, as is ensuring proper authentication setup with SPF, DKIM, and DMARC. Remember that IP warming and domain reputation building are ongoing processes, not one-time tasks. Staying vigilant with your metrics and proactively addressing any deliverability issues will safeguard your email program's success. By following these best practices, you can navigate your ESP migration smoothly, ensuring your emails continue to land in the inbox and drive engagement.