Infrastructure
What is ESP (Email Service Provider)?
A platform that hosts mailboxes or sends email on your behalf, managing delivery infrastructure and authentication.
An ESP provides the infrastructure to send and/or receive email, including mail servers, sending IPs, authentication setup, and deliverability tooling. Examples range from mailbox providers like Google Workspace and Microsoft 365 to bulk and transactional senders. ESPs manage IP reputation, throttling, and feedback loops that individual senders usually cannot operate themselves.
Why it matters for cold email
Your ESP shapes deliverability through its IP pools, reputation, and how strictly it polices cold outreach, and some mailbox providers tolerate prospecting better than others. The receiving ESP (Gmail, Outlook) also decides inbox versus spam based on provider-specific signals you must tune for each one.
Related terms
Stop guessing at deliverability.
Scheduler Zero handles authentication, warmup, and sender reputation so your cold email lands in the inbox, not the spam folder.