Why are new email sending IPs problematic during a data center switch?

New IPs lack a sending history and established reputation with mailbox providers. Suddenly sending high volumes from them can trigger spam filters, leading to low inbox placement or even blocklisting, as providers see it as suspicious activity.

What is an active-active email sending setup, and how does it help in DR?

An active-active setup means both your primary and disaster recovery data centers (and their respective IP ranges) are continuously sending email traffic. This keeps the DR IPs warmed and maintaining a positive reputation, preventing a cold start if the primary site fails.

Should I contact mailbox providers before a DR test or data center switch?

Yes, it is highly recommended to proactively inform major mailbox providers like Google and Yahoo about your planned switch, especially if new IP ranges are involved. This can help them anticipate the change and potentially prevent deliverability issues.

What types of emails should be prioritized during a switch to new IPs?

During a switch to new IPs, prioritize critical transactional emails such as password resets, two-factor authentication codes, and order confirmations. These emails are highly anticipated and have good engagement, which helps build positive IP reputation quickly.

How long does it typically take to warm up new email sending IPs?

IP warmup is a gradual process that can take anywhere from a few weeks to several months. It depends on factors like your sending volume, recipient engagement, and the specific mailbox providers you're sending to. Sudden high volumes on new IPs can lead to blocklisting.

How should email sending IPs be handled during a data center switch disaster recovery test? - Sender reputation - Email deliverability - Knowledge base

Managing email sending IPs during a data center switch, especially for disaster recovery tests, presents a unique set of challenges. It's not just about getting systems back online, but ensuring your email deliverability remains uncompromised. The integrity of your sender reputation, built over time with consistent sending practices, hangs in the balance when public IP ranges shift.

A common scenario involves transitioning from a primary data center to a disaster recovery (DR) site, where the IP addresses (often hundreds of them) are entirely different. This situation can severely impact how mailbox providers, such as

Gmail and

Outlook, perceive your sending activity.

The core of the problem lies in the reputation associated with IP addresses. Mailbox providers track sending behavior and assign a reputation score to each IP. A sudden change to entirely new, 'cold' IPs can trigger spam filters, leading to emails being rejected, sent to spam folders, or even causing your new IPs to land on a blocklist (or blacklist).

Managing sender reputation with new IPs

When you have hundreds of IPs, each sending volumes ranging from 100,000 to 300,000 emails per day from your primary site, switching to a completely new set of IPs in a DR scenario is akin to starting your sender reputation from scratch. Mailbox providers will see high volume from unknown IPs, which is a major red flag for potential spam. This can quickly lead to your new IPs being added to a blocklist (blacklist), severely hindering your deliverability.

IP warmup is a gradual process of increasing email volume over time on new IP addresses, allowing mailbox providers to build a positive reputation for them. This process typically takes weeks or even months, depending on the volume and recipient engagement. Attempting to send full volumes from cold IPs without proper IP warmup strategies can result in significant inbox placement issues and damage your sender reputation.

The critical takeaway is that IP reputation is not transferable. Even if your domain reputation is strong, a sudden shift to unknown IP addresses will necessitate a new reputation-building phase for those IPs. This is why careful planning is essential to avoid email deliverability problems during a data center switch.

Strategic approaches for IP handling

There are several strategies to consider when handling email sending IPs during a data center switch, especially if your network team states that public IP ranges cannot be moved between data centers. The ideal, though often complex, solution is to maintain the same IP addresses using Border Gateway Protocol (BGP) rerouting, if you own your own IP space and have an Autonomous System (AS) assigned. This allows you to announce your IP blocks from the active data center, keeping your sender reputation intact. Cisco discusses keeping IP addresses during disaster planning scenarios.

If BGP rerouting isn't an option, a robust approach is to run an active-active email sending setup across both your main and DR data centers. In this model, both data centers (and their respective IP ranges) are continuously sending email, even if at a lower volume. This ensures that the IPs in your DR site are consistently warmed up and maintain a sender reputation, preventing a cold start during a disaster or test.

However, if you're transitioning to entirely new IPs in the DR site without prior warming, you face the challenge of immediate deliverability degradation. During a site switch, emails often originate from different IPs than those previously used. This new set of IPs will not have any established reputation.

In a true disaster scenario, some level of deliverability disruption is almost inevitable. The goal is to minimize this impact. One crucial step is to proactively alert major mailbox providers and email security vendors about your impending data center switch or disaster recovery test. This communication can help them understand the sudden change in sending patterns and potentially whitelist your new IP ranges, reducing the likelihood of immediate blocklisting (blacklist entries) or throttling.

Proactive reputation management

Consistent sending volume: IPs in both data centers are always sending some email volume.
Pre-warmed IPs: No cold IPs mean less risk of sudden reputation drops.
Reduced sudden impact: Gradual increase in volume from the DR site during a switch.

Reactive challenges

Requires rapid IP warmup: Intense effort to build reputation quickly.
Potential immediate deliverability hits: Risk of emails landing in spam or being rejected.
Reliance on postmaster communication: Proactive alerts are crucial but not a guarantee against all issues.

Minimizing impact on deliverability

When facing an unavoidable switch to new, un-warmed IPs, prioritize your most crucial email types first. This includes transactional emails like password resets, order confirmations, and security alerts. These messages are expected by recipients and typically have higher engagement rates, which can help build a positive reputation for the new IPs more quickly.

For any non-critical email, such as marketing campaigns, you must initiate a proper IP warmup strategy for the new IP addresses. Start by sending very small volumes (e.g., less than 10,000 emails per day per IP) to your most engaged and active recipients. Gradually increase the volume and broaden your recipient list over several days or weeks. This cautious approach signals to mailbox providers that you are a legitimate sender.

Structured IP warm-up for DR

Even during a DR test or actual disaster, a structured warm-up can significantly mitigate deliverability issues, especially for less critical email streams. Focus on building trust incrementally.

Day 1-3: Send 1,000 emails/IP to highly engaged recipients (e.g., recent logins, critical alerts).
Day 4-7: Increase to 5,000 emails/IP, expanding to slightly less engaged but still active users.
Week 2-4: Continue gradual increases, monitoring metrics closely, for other email types. This process will vary depending on your typical volume and engagement.

Establishing a communication protocol with major mailbox providers is a proactive measure that can make a difference. Inform them in advance about planned data center switches or DR tests, especially if new IP ranges will be used. Providing them with the new IP addresses and an explanation of the temporary shift can help prevent them from mistakenly blocklisting (or blacklisting) your new sending infrastructure. This is not an unusual request for them.

While some deliverability issues might still occur in a true disaster scenario, these preparatory steps and proactive measures can significantly reduce the severity and duration of any impact. Continuous DMARC monitoring and blocklist monitoring are also essential during and after a switch to quickly identify and address any problems.

Record type	Purpose	Example
MX (Mail Exchange)	Directs incoming email to your mail servers.	MX example.com 10 mail.example.com
A (Address)	Maps domain names to IP addresses for mail servers.	mail.example.com A 203.0.113.45
SPF (Sender Policy Framework)	Authorizes sending IPs for your domain, preventing spoofing.	TXT @ "v=spf1 ip4:203.0.113.0/24 ~all"
DKIM (DomainKeys Identified Mail)	Digitally signs outgoing emails for authenticity verification.	selector1._domainkey TXT "v=DKIM1; p=..."
DMARC (Domain-based Message Authentication, Reporting & Conformance)	Specifies policy for failed SPF/DKIM authentication.	_dmarc TXT "v=DMARC1; p=none; ruf=..."

Views from the trenches

Best practices

Implement an active-active email sending setup across data centers to keep IPs consistently warmed.

Proactively alert major mailbox providers, such as Microsoft and Yahoo, about planned data center switches or DR tests.

Prioritize the sending of critical transactional emails (like password resets) on any new IPs first to build reputation quickly.

Common pitfalls

Switching all email volume immediately to cold (un-warmed) IP addresses in a new data center.

Underestimating the time and effort required to warm up new IP ranges, which can take weeks or months.

Failing to communicate with mailbox providers about significant infrastructure changes.

Expert tips

Warmup is a time-consuming process that can take weeks or months, so plan accordingly.

Focusing on the most crucial emails first during a disaster recovery scenario can help mitigate immediate deliverability issues.

Contacting postmasters at major providers is a proactive step that can help manage expectations and prevent unwarranted blocklisting.

Expert view

Expert from Email Geeks says that warmups take a significant amount of time, suggesting exploring options like BGP rerouting if you own your IP space and have an Autonomous System, to avoid starting cold.

2022-05-16 - Email Geeks

Expert view

Expert from Email Geeks recommends prioritizing the most crucial emails, such as password resets and transactional mail, during disaster recovery. For other mail, a slow warm-up starting with engaged recipients is necessary.

2022-05-16 - Email Geeks

Ensuring business continuity for email

Successfully navigating email sending IPs during a data center switch disaster recovery test requires a comprehensive strategy that prioritizes deliverability and sender reputation. Whether through BGP rerouting, an active-active setup, or meticulous IP warmup and postmaster communication, planning is key to mitigating risks.

Ultimately, the goal is to ensure business continuity for your email communications, even in the face of significant infrastructure changes or unexpected disasters. Proactive measures, thorough testing, and a clear understanding of how mailbox providers perceive your sending infrastructure will safeguard your email program and maintain trust with your recipients.