Why would identical traffic patterns be a concern during an SMTP migration?

The potential concern arises because spam filters look for unusual or sudden changes in sending patterns, which could indicate malicious activity. Identical traffic from two different sources might, in some cases, trigger suspicion.

Does moving from a shared domain to custom domains mitigate this risk?

While there's a minor risk, moving to custom domains for each client is generally seen as a positive step. It allows for better reputation management for individual senders, reducing the collective risk associated with a shared domain. A gradual warming process on the new IPs helps mitigate initial concerns.

Do I still need to warm up my IPs if I'm moving to a shared IP pool?

It is best practice to always warm up new IP addresses, even if you are moving into a shared IP pool. This process builds trust with mailbox providers and signals legitimate sending behavior.

What metrics should I monitor to ensure a successful migration?

Monitor inbox placement rates, bounce rates, spam complaint rates, and blocklist (or blacklist) status. Use tools like Google Postmaster Tools and analyze your DMARC reports to track performance and identify issues early.

Should I be concerned about identical traffic patterns when migrating to a new SMTP provider? - Sender reputation - Email deliverability - Knowledge base

Q: What role does email authentication play during this migration?

Yes, ensure all email authentication records (SPF, DKIM, and DMARC) are correctly configured for your new SMTP provider and the custom domains. These records are crucial for verifying your sender identity and preventing spoofing.

When migrating your email sending infrastructure to a new SMTP provider, it is natural to consider how the transition might impact your email deliverability. A common concern that arises is whether identical traffic patterns, particularly during a period where both the old and new providers are active, could trigger spam filters or negatively affect your sender reputation.

The transition from a shared domain on an old SMTP to individual custom domains on a new provider represents a strategic shift. While it introduces a temporary overlap in traffic, the underlying goal is to establish a stronger, more distinct sending identity for each client. This approach aims to reduce reliance on a common shared domain, ultimately leading to better control over individual client sending reputation.

Understanding how mailbox providers perceive this dual-sending scenario is crucial for ensuring a smooth migration. The potential impact hinges on various factors, including the volume of parallel traffic, the number of distinct sending sources, and how meticulously the transition is managed.

Understanding SMTP migration and reputation

Migrating to a new SMTP provider inherently means introducing new sending IP addresses, even if you are moving into a shared IP pool. Mailbox providers, such as

Google and

Yahoo, closely monitor traffic from new IPs to prevent spam. This is why a proper IP warming process is essential, gradually increasing email volume to build trust. The transition from a common shared domain to individual custom domains also plays a significant role in how your sending reputation is perceived.

While a temporary overlap where both the old and new SMTPs send from the same client domain might seem risky, the shift to custom domains is generally beneficial. It allows each client to build their own dedicated sender reputation, distinct from the collective reputation of a shared domain that could be influenced by other users. This segregation can improve overall deliverability and reduce the risk of being affected by poor practices of others.

Positive aspects of custom domains

Moving to custom domains (or dedicated domains) for each client is a sound strategy for long-term email deliverability. It gives each client greater control over their sender reputation and reduces the potential impact of other senders on a shared domain. This can lead to more stable inbox placement and less exposure to broad blocklists (or blacklists).

Independent reputation: Each client's sending performance directly impacts their own domain reputation.
Reduced shared risk: Poor sending practices by other users on a shared domain will not negatively affect your client's deliverability.
Improved trust: Mailbox providers often favor authenticated sending from well-maintained, unique domains.

Analyzing traffic patterns and their impact

Spam filters are sophisticated systems designed to detect anomalies. While identical traffic patterns from two distinct SMTP providers for a short period might raise an eyebrow, the context of a migration is usually understood. Mailbox providers, especially large ones, can recognize legitimate shifts in email infrastructure.

The key differentiation lies in the nature of the 'identical traffic'. If you were sending from hundreds of disparate sources and suddenly migrated all that volume identically, it could be a flag. However, if the pattern is simply a temporary overlap between an old shared domain and new, separate custom domains, the risk is significantly lower. The transition to dedicated domains for each client is a positive signal in the long run, indicating a more responsible sending practice.

It is worth noting that some mailbox providers, like

Microsoft, can be particularly sensitive to new or changing sending patterns. A gradual approach to shifting volume, even when moving to a shared IP pool initially, is often recommended. This allows their systems to observe and build trust in your new sending infrastructure. If you experience unexpected issues, you may need to troubleshoot migration issues that arise.

High risk patterns

Sudden volume spike: Immediately shifting all traffic to a new, un-warmed IP or IP pool.
Disparate sources: Sending a high volume of email from many different, previously unknown IP addresses simultaneously.
Unauthenticated sending: Lack of proper authentication records like SPF, DKIM, and DMARC.

Lower risk scenarios

Gradual volume shift: Incrementally increasing volume on new IPs while decreasing on old IPs.
Domain-specific sending: Migrating clients to their own custom sending domains instead of a shared one.
Consistent content: Maintaining similar email content and audience engagement during the migration.

Strategies for a smooth transition

To minimize any potential negative impact, a carefully planned migration strategy is essential. This typically involves a phased rollout, allowing you to gradually shift email volume from your old SMTP provider to the new one. This gradual increase helps the new IP addresses and domains build a positive sending reputation with mailbox providers over time.

Ensuring proper email authentication (SPF, DKIM, DMARC) is paramount. These records tell receiving mail servers that your emails are legitimate and authorized. When migrating, ensure these DNS records are correctly configured for your new SMTP provider and the custom domains. Improper configuration can lead to deliverability issues, including emails going to spam or being outright rejected.

Consider the following example of SPF and DKIM records you might need to add or update during your migration:

SPF record example for new providerDNS

v=spf1 include:_spf.newprovider.com ~all

DKIM record example for custom domainDNS

k1._domainkey.yourclientdomain.com. IN TXT "v=DKIM1; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDy..."

Another strategy is to align your email sending volume with your new SMTP provider's recommendations. Many providers offer detailed warming schedules. Adhering to these, even with a temporary dual-sending setup, can significantly reduce the risk of your emails being flagged as suspicious. For more specific guidance on migrating to a cloud ESP, consulting their documentation is advisable.

Monitoring and mitigation during migration

Throughout the migration process, continuous monitoring of your email deliverability is non-negotiable. This involves tracking key metrics to identify any drops in inbox placement, increases in bounce rates, or spikes in spam complaints. Pay close attention to feedback loops from major mailbox providers.

Tools like Google Postmaster Tools and similar offerings from other providers can give you insights into your sender reputation, spam rates, and deliverability trends for emails sent to their users. Regularly checking IP and domain blocklists (or blacklists) is also important. If you notice a sudden increase in being listed on a blocklist, it indicates an issue that needs immediate attention.

If you do encounter deliverability issues, such as emails going to spam when migrating, it is important to diagnose the problem quickly. This might involve reviewing your email content, list hygiene, authentication records, and sending patterns. Being proactive in your monitoring and responsive to any red flags can help you maintain a strong sender reputation throughout the migration and beyond.

Metric	What to monitor	Why it matters
Inbox placement rate	Percentage of emails delivered to the inbox versus spam/junk.	Direct indicator of deliverability performance.
Bounce rate	Hard and soft bounces for new and old IPs.	High rates suggest list quality or IP trust issues.
Spam complaint rate	Percentage of recipients marking your emails as spam.	A critical metric; high rates severely damage reputation.
Blocklist status	Regularly check if your sending IPs or domains are listed.	Being listed can prevent emails from reaching the inbox.
DMARC reports	Analyze aggregate and forensic reports for authentication failures.	Helps identify misconfigurations or unauthorized sending.

Views from the trenches

Best practices

Maintain consistent email content and list segmentation during the migration period.

Implement a gradual IP warming schedule tailored to your new SMTP provider's recommendations.

Thoroughly configure and verify all DNS records (SPF, DKIM, DMARC) for new domains.

Actively monitor deliverability metrics and feedback loops for both old and new sending setups.

Segment your audience and send smaller, highly engaged batches initially from the new setup.

Common pitfalls

Abruptly switching all email volume to new IPs without a proper warming period.

Neglecting to update or incorrectly configuring SPF, DKIM, or DMARC records.

Ignoring feedback loop data or allowing spam complaint rates to rise unchecked.

Maintaining identical email volume from two distinct SMTP providers for an extended period.

Failing to clean email lists, leading to high bounce rates on new sending infrastructure.

Expert tips

For challenging mailbox providers, like Microsoft, a dedicated IP might offer an edge even if shared pools are generally sufficient.

Consider a phased approach where low-engagement emails move first, followed by higher-engagement campaigns.

Utilize Postmaster Tools from major ISPs to gain deeper insights into your new IP and domain reputation.

Document every step of your migration, including volume changes and DNS updates, for easier troubleshooting.

Keep the old SMTP active with minimal volume for a transition period, gradually phasing it out.

Expert view

Expert from Email Geeks says that having hundreds of sources for new traffic can be concerning, but only two sources are not as worrying.

2024-04-29 - Email Geeks

Expert view

Expert from Email Geeks notes that shared versus dedicated domains are probably not a concern in terms of identical traffic patterns.

2024-04-29 - Email Geeks

Navigating your SMTP migration

The concern about identical traffic patterns when migrating to a new SMTP provider is valid, but often less critical than anticipated, especially when moving towards a more granular, domain-specific sending setup. The shift from a shared domain to individual client domains is a positive step for long-term deliverability and sender reputation.

By implementing a gradual migration strategy, ensuring robust email authentication, and vigilantly monitoring key deliverability metrics, you can navigate this transition smoothly. While some temporary overlap is unavoidable, the benefits of establishing independent, well-managed sending reputations for each client far outweigh the transient risks.