What are the deliverability risks of setting up a sender domain on a different ESP?

Key findings

• New domain status: Any newly registered domain (especially those less than six months old) is often viewed with suspicion by mail filters, regardless of the ESP or IP.
• IP and domain warming: New IPs and sender domains require a careful warm-up period to build a positive reputation, especially when used for bulk sending.
• Domain type preference: Using a subdomain (e.g., email.company1.com) is generally safer and can potentially confer some reputation from the parent domain, unlike a lookalike or 'cousin' domain (e.g., email-company1.com), which can appear suspicious.
• Reputation linkage: While separate IPs and domains limit direct reputation transfer, linking to or mentioning a domain with a bad reputation within email content can still cause deliverability issues. Similarly, if the sending infrastructure's reputation is poor, it may impact any domain sending through it.

Key considerations

• Careful planning: A detailed strategy for domain and IP setup, including a robust warming plan, is essential to mitigate risks.
• Engagement focused warming: Warm-up processes are most effective with highly engaged recipients, which can be challenging for a brand new domain.
• Sender reputation monitoring: Continuously monitor domain and IP reputation across all sending entities to identify and address issues promptly.
• Authentication setup: Ensure proper SPF, DKIM, and DMARC records are configured for the new sender domain on the new ESP. This is critical for authentication and trust.

Key opinions

• No simple answer: The deliverability risks are multi-factorial and depend on specific setup details.
• New domain warm-up: A new sender domain, even with separate IPs, requires a significant warm-up period (potentially 3+ months) before sending bulk emails.
• Cousin domains are risky: Using a 'cousin' or lookalike domain (e.g., company1-cousin.com) is generally seen as problematic and suspicious by filters.
• Subdomain preference: A subdomain (e.g., email.company1.com) is the preferred approach as it's less suspicious and can potentially inherit some of the parent domain's good reputation.
• Indirect reputation impact: While separate IPs isolate direct reputation, linking to a poorly reputed domain or company within emails can still pose risks.

Key considerations

• Dedicated IPs: Ensuring the new sender domain uses dedicated IPs within the new ESP helps isolate its reputation from other sending entities.
• Domain age: Be aware that newly registered domains (under 6 months) are scrutinized more heavily by filters.
• Engaged recipients for warm-up: Successful IP and domain warming requires sending to a list of highly engaged recipients, not just non-bouncing ones.
• Due diligence on new ESP: Verify the new ESP's platform health and deliverability practices, as they set the stage for your sending success. More information can be found on Customer.io.

Key opinions

• Domain and IP separation benefits: Maintaining entirely separate IPs and sender domains for each company minimizes the risk of one's poor sending practices directly affecting the other's reputation.
• New domain challenges: Regardless of ESP, a newly introduced sender domain needs to build its own reputation from scratch, which is a slow and delicate process.
• Subdomain as best practice: Using a subdomain of the primary domain (e.g., marketing.company1.com) is generally recommended over creating a new, similar-looking domain to leverage existing brand trust and potential reputation inheritance.
• Content and linking impact: Even with separate infrastructure, emails that link to or mention domains with poor reputations can be flagged by spam filters, creating an indirect deliverability risk.
• Authentication is key: Proper configuration of SPF, DKIM, and DMARC is non-negotiable for establishing trust and verifying sender authenticity, regardless of which ESP hosts the domain. This is covered in Mailgun's deliverability guide.

Key considerations

• Cautious warm-up: The warming process for a new domain on a new ESP should be meticulously gradual, focusing on sending to highly engaged subscribers first.
• Engagement matters: Mailbox providers heavily weigh subscriber engagement in their reputation algorithms. Low engagement on a new domain can quickly lead to poor inbox placement.
• Shared vs. dedicated IP: While the query specifies dedicated IPs, understand that shared IP pools introduce reputation risks from other senders, which may be a consideration when evaluating an ESP's infrastructure.
• DMARC monitoring: Actively monitoring DMARC reports can provide insights into authentication failures and potential deliverability issues on the new domain.

Key findings

• Authentication standards: SPF, DKIM, and DMARC are critical for verifying sender identity and ensuring messages are not perceived as spoofed or fraudulent.
• Sender reputation building: A good sender reputation is built over time through consistent, legitimate sending, low complaint rates, and high engagement from recipients.
• IP warming importance: When using a dedicated IP (whether new or previously used by another sender), a structured IP warming process is required to establish trust with ISPs.
• Domain age sensitivity: New domains are generally treated with higher scrutiny by spam filters to prevent abuse from transient senders.

Key considerations

• Maintain list hygiene: Regularly clean email lists to remove inactive users, spam traps, and invalid addresses, which can negatively impact reputation.
• Consistent sending practices: Sudden spikes or drops in sending volume can raise red flags. Maintain a steady and predictable sending pattern, especially for new domains.
• Monitoring deliverability metrics: Pay close attention to bounce rates, complaint rates, and engagement metrics (opens, clicks) as reported by your ESP and postmaster tools.
• Compliance with guidelines: Adhere to the sending guidelines of major mailbox providers (like Gmail and Yahoo) and industry best practices to ensure long-term deliverability.