Multi-ESP Deliverability Audit: Untangling Three Platforms

The Challenge

VacationVIP was operating across three email service providers simultaneously: HubSpot, SendGrid, and Customer.io. Each platform had been set up independently at different points in the company's growth, and none of them were coordinated with each other.

The result was a deliverability mess. DMARC was set to p=none, which meant the domain had no protection against spoofing and mailbox providers had no clear signal about which sending sources were legitimate. SPF and DKIM records were incomplete or conflicting across the three platforms. Some sends were authenticated properly, others were not, and there was no unified view of what was happening.

Our Approach

Comprehensive Deliverability Audit

We conducted a full audit across all three ESPs, examining:

Authentication Records: We mapped every SPF, DKIM, and DMARC record associated with their sending domains. We identified conflicts, gaps, and misconfigurations across HubSpot, SendGrid, and Customer.io. When three platforms are sending from the same domain with incomplete authentication, mailbox providers cannot reliably verify the legitimacy of any of them.

DMARC Analysis: The DMARC policy was set to p=none, which is effectively the same as having no DMARC at all. This meant that even if someone spoofed their domain, no receiving server would take action. It also meant that ISPs had no confidence in the domain's sending practices, which directly impacted inbox placement.

Sending Patterns and Reputation: We analyzed the sending volume, frequency, and engagement metrics from each ESP to understand how each platform was contributing to (or degrading) the overall domain reputation.

Infrastructure Overlap: We identified where the three ESPs were stepping on each other, sending to the same contacts, competing for inbox attention, and creating inconsistent subscriber experiences.

Remediation Plan

Based on the audit findings, we developed a comprehensive remediation plan covering:

• Unified authentication across all three ESPs with proper SPF alignment, dedicated DKIM signing for each platform, and a phased DMARC enforcement roadmap moving from p=none to p=quarantine to p=reject
• Sending domain strategy to reduce conflicts between platforms
• List hygiene and deduplication across ESPs
• Monitoring and reporting framework to maintain deliverability long-term

Audit Findings

The audit, delivered at $1,500, revealed that VacationVIP's deliverability issues were not caused by any single platform but by the lack of coordination between all three. The full implementation of the remediation plan was scoped at $5,000.

The core finding applies to any company running multiple ESPs: without unified authentication and a coordinated sending strategy, adding more platforms makes deliverability worse, not better. Each new ESP introduces additional complexity that, if unmanaged, compounds into systemic inbox placement problems.