An email service provider (ESP) is a service for sending email in bulk, such as newsletters, product updates and receipts. Mailchimp, SendGrid and Brevo are examples. They send from their own infrastructure and handle unsubscribes and bounces.
ESPs and mailbox providers
- ESPs send many emails to people who signed up. Most forbid cold email in their terms, because complaints from unsolicited email damage their shared IPs.
- Mailbox providers (Google Workspace, Microsoft 365) give each person a real mailbox for one-to-one email.
Which cold email uses
Cold email goes out from mailboxes: a modest number of personal emails a day from each, through a tool that spreads sending across many mailboxes and handles replies and follow-ups. That's how mailzy works: real mailboxes, connected or bought, with campaigns, warm-up and replies in one place.