What is an email relay service, and should you use one?

An email relay service accepts outgoing messages from your systems and delivers them through their infrastructure. Examples include SendGrid, Mailgun, Amazon SES, and Postmark.

What relays provide:

Established sending infrastructure

IP pools with existing reputation

Delivery optimization and retry logic

Analytics and bounce processing

Technical compliance (reverse DNS, rate limiting)

Cold email considerations:

Most relay services prohibit cold email in their terms of service

Services that allow it may have shared IP pools that suffer from other senders' behavior

Your domain reputation still matters regardless of sending infrastructure

Violating terms risks account termination and data loss

Practical reality: Cold email tools typically connect directly to mailbox accounts (SMTP through Gmail, Outlook, or Google Workspace) rather than using relay services. This mimics individual sending but limits volume. Choose infrastructure that explicitly supports your use case.