Introduction
Understand what mail servers do, how sending and receiving differ, and where hosted providers and MailKite fit.
Reviewed
A mail server accepts, routes, stores, or delivers email. Those are different jobs: a delivery platform for application notifications is not necessarily a mailbox server that someone can connect to with a mail client.
Follow a message
- A mail client or application submits a message to a sending service using SMTP or an HTTP API.
- A mail transfer agent (MTA) queues it, looks up the recipient domain’s MX records, and attempts delivery over SMTP. Temporary delivery failures can cause retries.
- The receiving system checks its recipient and security policies, then accepts or rejects the message.
- Accepted mail goes to a mailbox, another mail server, or an application integration such as a webhook.
SMTP moves messages. IMAP lets a client read a stored mailbox. An HTTP API provides application-specific operations, such as sending or reading messages; it is not a universal mail-server protocol. A webhook delivers an event to your application when something happens.
Choose the job before the software
| Your goal | Start with | What you still need to check |
|---|---|---|
| Run employee mailboxes | A mailbox suite or enterprise mail platform | Identity, clients, storage, backups, policy, and support |
| Deliver application email | A delivery platform or email service provider | Sender authentication, recipient permissions, bounces, and delivery limits |
| Turn incoming email into application events | Inbound routing with a webhook/API | Signature verification, durable handling, retries, and attachment policy |
| Give an agent an inbox | A mailbox/API service with appropriate access controls | Scoped credentials, thread handling, untrusted content, and approval gates |
An ESP operates delivery infrastructure for you. A self-hosted server gives you operational control, but also responsibility for patching, DNS, monitoring, queues, abuse handling, and reputation. Open-source software can also have commercial support; these categories overlap rather than describe mutually exclusive licenses.
Where MailKite fits
MailKite lets applications receive email through a webhook and send through an API. Use the product quickstart if your goal is application email without running a server. If you already operate mail infrastructure, use these guides to understand which jobs stay on that system and which can be delegated.
Changing a domain’s MX records changes where new incoming mail goes. Do not replace a production mailbox system’s MX records merely to test an application integration. Start with a separate verified domain/subdomain or an explicit forwarding route.
Continue by category
Read open-source mail servers, enterprise mail services, email service providers, or agent mail providers.
For protocol background, see SMTP (RFC 5321) and IMAP4rev2 (RFC 9051).