How Does Email Work? From Send to Inbox, Explained

Email can feel like one instant action, but it is really a chain of small steps. Once you know the path from Send to inbox, setup terms like outgoing server, incoming server, and sync make a lot more sense.

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Christin Baumgarten

Operations Manager

Michael Bodekaer
Reviewer

Founder, Board Member

Abdessamad El Bahri
Tester

Full Stack Engineer

Authored By Christin Baumgarten Operations Manager

Christin Baumgarten is the Operations Manager at Mailbird, where she drives product development and leads communications for this leading email client. With over a decade at Mailbird — from a marketing intern to Operations Manager — she offers deep expertise in email technology and productivity. Christin’s experience shaping product strategy and user engagement underscores her authority in the communication technology space.

Reviewed By Michael Bodekaer Founder, Board Member

Michael Bodekaer is a recognized authority in email management and productivity solutions, with over a decade of experience in simplifying communication workflows for individuals and businesses. As the co-founder of Mailbird and a TED speaker, Michael has been at the forefront of developing tools that revolutionize how users manage multiple email accounts. His insights have been featured in leading publications like TechRadar, and he is passionate about helping professionals adopt innovative solutions like unified inboxes, app integrations, and productivity-enhancing features to optimize their daily routines.

Tested By Abdessamad El Bahri Full Stack Engineer

Abdessamad is a tech enthusiast and problem solver, passionate about driving impact through innovation. With strong foundations in software engineering and hands-on experience delivering results, He combines analytical thinking with creative design to tackle challenges head-on. When not immersed in code or strategy, he enjoys staying current with emerging technologies, collaborating with like-minded professionals, and mentoring those just starting their journey.

How Does Email Work? From Send to Inbox, Explained
How Does Email Work? From Send to Inbox, Explained

Email can feel like one instant action, but it is really a chain of small steps. Once you know the path from Send to inbox, setup terms like outgoing server, incoming server, and sync make a lot more sense.

TL;DR

Short answer: when you send an email, your app creates a standard message, submits it with SMTP to an outgoing mail server, that server looks up the recipient domain’s MX record in DNS, delivers the message to the recipient’s mail server, and the recipient’s app then reads or syncs it from that server, for example with IMAP. [1] [2] [3] [4] [5] [6]

  • Your app creates a standard message with headers such as From, To, Date, and Subject, plus the message body.
  • Pressing Send usually means submitting the message to an outgoing mail server with SMTP.
  • The sending server asks DNS for the recipient domain’s MX records.
  • Mail servers relay the message with SMTP and can queue it and retry later when a problem is temporary.
  • The recipient server stores accepted mail in a mailbox on the server.
  • IMAP is designed for reading and syncing mail that stays on the server, while POP3 is mainly for retrieving mail by downloading it.
Table of contents

What happens when you send an email?

Think of email as six jobs: compose the message, submit it, find the destination, relay it, store it, then sync it to the reader’s app.

1 Compose Your app builds the message.
2 Submit SMTP hands it to the outgoing server.
3 Look up DNS finds the recipient domain’s MX record.
4 Relay Servers transfer the message with SMTP.
5 Store The recipient server saves it in a mailbox.
6 Sync The recipient app reads it, usually through IMAP.
Read it left to right: client → SMTP submission → DNS/MX lookup → recipient mail server → mailbox → IMAP sync. POP3 can retrieve mail too, but its normal model is more download-focused than sync-focused. [1] [2] [3] [4] [6]

  1. Your app builds the message

    When you write an email, your app creates a standard message format. That message includes headers such as From, To, Date, and Subject, plus the message body. [5]

  2. Pressing Send usually means “submit this to my outgoing server”

    Your app usually does not contact the recipient directly. It hands the message to an outgoing mail server, and that submission step uses SMTP. [1] [2]

  3. The sending side asks where the recipient’s domain receives mail

    The part after the @ is the destination domain. The sending server asks DNS for that domain’s MX records, which identify the host that accepts mail for it. [2] [3]

  4. One mail server relays the message to another

    Using the MX result, the sending server opens an SMTP connection to the recipient’s mail server and transfers the message. If the issue is temporary rather than permanent, the usual behavior is to queue the message and retry later. [2]

  5. The recipient server stores the message in a mailbox

    Once the receiving server accepts the message, it stores it in the recipient’s mailbox on the server. That is why a message can be delivered before the person has actually opened it. [2] [4]

  6. The recipient’s app reads or syncs what is stored there

    The last step is access, not transport. IMAP is designed for working with mail that stays on the server and for resyncing folders and state, while POP3 is mainly for retrieving mail from the server, usually by downloading it. [4] [6]

How email works: quick examples

Simple example

You send a note from alex@example.com to maya@company.net . Your app submits it with SMTP, the sending server checks company.net ’s MX records, the recipient server accepts it, and Maya sees it when her app syncs the mailbox. [1] [2] [3] [4]

Two-device example

You read a thread on your phone in the morning, then archive it in Mailbird on your laptop later. With IMAP, both apps are working from the same server-side mailbox, so the state can stay in sync. [4]

Delay example

You hit Send at 8:59 AM, but the other person gets the message at 9:12 AM. A temporary DNS or server problem can cause the sending side to queue the message and try again later instead of failing right away. [2]

Email protocols explained: SMTP, IMAP, POP3, DNS, and MX

These are the main terms behind how email works from Send to inbox.

Email client

The email client you use to write and read email, such as Mailbird.

SMTP

Simple Mail Transfer Protocol. It is used to submit mail from your app and relay mail between mail systems. [1] [2]

DNS

The naming system that stores records for a domain, including where that domain receives email. [3]

MX record

The DNS record that points sending mail systems to the host that accepts email for a domain. [3]

Mail server

The mail server is the system that accepts, stores, and passes along email messages. [2] [4]

Mailbox

The server-side place where accepted messages wait until an app reads or syncs them. [4]

IMAP

Internet Message Access Protocol. It is used to access and sync mail that stays on the server. [4]

POP3

Post Office Protocol version 3. It retrieves mail a server is holding, usually by downloading it. [6]

Common misconceptions

Most confusion comes from mixing up the app you see with the servers doing the transport and storage.

  • “My email app sends mail straight to the other person’s phone.”
    Usually no. Your app normally submits the message to a sending server first, and mail servers handle the rest of the route. [1] [2] [4]
  • “SMTP and IMAP do the same job.”
    No. SMTP sends or submits mail. IMAP reads and syncs mail that is already stored on the server. POP3 retrieves it in a more download-centered way. [1] [2] [4] [6]
  • “My inbox lives inside the app.”
    With IMAP, the mailbox lives on the server and the app syncs with it. [4]
  • “The part after the @ is just branding.”
    That domain tells the sending side which domain to query for MX records. [2] [3]
  • “If an email does not arrive instantly, it failed.”
    Not always. Temporary problems can lead to queueing and retry, so delay does not automatically mean failure. [2]
  • “POP3 syncs the same way IMAP does.”
    Not really. IMAP is built around server-based access and resync, while POP3 is mainly built around retrieval. [4] [6]

Frequently Asked Questions

What happens the moment I press Send?

Your app submits the message to an outgoing mail server. That server then looks up the recipient domain and relays the message to the recipient’s mail server.

Sources: [1] [2] [3]

Does email go straight from my computer to the other person’s phone?

Usually no. It normally goes through mail servers first, and the other person’s device reads or syncs from their server mailbox.

Sources: [1] [2] [4]

What’s the difference between SMTP and IMAP?

SMTP is for sending or submitting mail. IMAP is for reading and syncing mail that is stored on the server.

Sources: [1] [2] [4]

What does an MX record do?

It tells sending mail systems which host accepts email for a domain.

Sources: [3]

Why do some emails arrive late?

Temporary DNS or server problems can cause the sending side to queue the message and retry later.

Sources: [2]

Is IMAP better than POP3 for multiple devices?

Usually, yes. IMAP is built to keep mail on the server and resync state across clients, while POP3 is more download-focused.

Sources: [4] [6]

Does deleting an email on one device delete it everywhere?

With IMAP, changes usually sync through the server. With POP3, behavior can vary because the underlying model is different.

Sources: [4] [6]

Try it in Mailbird

Want this to click fast? Add an account in Mailbird, send yourself a test message, then open the same mailbox on another device. That lets you see the same path in real life: SMTP sends it out, the server stores it, and IMAP syncs it back. [1] [2] [4]

Sources

  1. IETF RFC 6409: Message Submission for Mail
  2. IETF RFC 5321: Simple Mail Transfer Protocol
  3. IETF RFC 1035: Domain Names - Implementation and Specification
  4. IETF RFC 9051: Internet Message Access Protocol (IMAP) - Version 4rev2
  5. IETF RFC 5322: Internet Message Format
  6. IETF RFC 1939: Post Office Protocol - Version 3