Definition
An ESP relay accepts email from your systems and delivers it through its own infrastructure, handling SMTP, throttling, authentication, and reputation.
Choosing a relay with strong infrastructure and reputation is a deliverability decision.
The ESP relay is the infrastructure your delivery depends on, so its health shapes your results. Choosing a provider with strong infrastructure and reputation is strategic. Monitoring throughput and placement keeps you informed.
What a Relay Provides
Routing, retries, authentication, and IP management.
Deliverability depends heavily on the relay's reputation.
Why It Matters
The ESP relay is the infrastructure your delivery depends on. Understanding it helps you choose and monitor the right provider.
Best Practices
- Evaluate relay uptime, throughput, and retry behaviour.
- Check that the relay enforces SPF, DKIM and DMARC.
- Monitor deliverability dashboards per IP pool.
- Check that the relay enforces SPF, DKIM, and DMARC.
- Ask about shared-IP vetting.
- Test the relay before committing.
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Related Glossary Terms
Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
Alt Text
Alt text is the written alternative to an image in an email, displayed when images are blocked, slow to load, or consumed by screen readers.
AOL Mail for Email Marketers
AOL Mail is a legacy email provider with specific deliverability requirements and rendering quirks, now operating as part of the Yahoo+AOL network under shared infrastructure.
Email Authentication Protocols
Email authentication protocols are technical standards that verify the identity of an email sender, helping mailbox providers distinguish legitimate mail from spam and phishing.
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Classification
Bounce classification uses SMTP codes (550, 551, 552, 553, 554, 450, 451, 452) and enhanced status codes to categorise permanent and transient delivery failures.
Frequently Asked Questions
It routes your email to recipients using its IPs and infrastructure. The ESP relay is the infrastructure your delivery depends on, so its health shapes your results.
A relay focuses on delivery; inboxing focuses on testing placement. Choosing a provider with strong infrastructure and reputation is strategic.
Yes, with dedicated IPs, at higher cost and effort. Monitoring throughput and placement keeps you informed.
Its infrastructure and reputation shape deliverability. The ESP relay is the infrastructure your delivery depends on, so its health shapes your results.
Uptime, throughput, retry, and reputation. Choosing a provider with strong infrastructure and reputation is strategic.