How Does an Email Message Flow from Sending to Delivery?
1 min read
How Does an Email Message Flow from Sending to Delivery?
1 min read
Guide Takeaways
Email delivery follows a standardized, multi-step flow using protocols like SMTP, POP, and IMAP.
After a message is composed (manually or via API), it’s handed off to a Mail Transfer Agent (MTA) for sending.
The MTA queries DNS to find the correct Mail Exchanger (MX) server for the recipient’s domain.
Sending and receiving servers communicate via SMTP to relay and accept the message.
Once accepted, the message becomes available for retrieval by the recipient’s email client.
POP downloads messages locally, while IMAP syncs them across all devices and keeps them on the server.
IMAP is the modern standard because it supports syncing, folders, and multi-device continuity.
Robust message flow relies on long-established email standards to achieve reliable global delivery.
Q&A Highlights
What protocol sends an email from one server to another?
SMTP (Simple Mail Transfer Protocol) is used to send and relay email.
How does a sending server know where to deliver an email?
It looks up the domain’s MX records via DNS to find the correct destination server.
What is an MTA?
A Mail Transfer Agent — the server responsible for sending email.
What is an MX server?
A Mail Exchanger — the receiving server designated to accept email for a domain.
What’s the difference between POP and IMAP?
POP downloads messages locally, while IMAP syncs them across all devices and keeps them on the server.
Why is IMAP more common today?
It supports multi-device syncing, folders, and persistent storage.
Do transactional emails follow the same flow?
Yes — they’re generated via API but still delivered using SMTP and standard email protocols.
What happens if the sending server can’t deliver the email?
It receives a bounce message from the MX server explaining the failure reason.
An email passes through multiple servers that help ensure it arrives at the right place. That email message flow uses a systematic process based on a number of long-established technical standards.
Understanding Email Message Flow, from Sending to Delivery
For most users, how an email message flows from the sender to a recipient’s inbox is something that happens behind the scenes. When an individual or an organization sends an email, the message travels from its point of origination, such as an email client where it was composed, across the Internet to its destination. Along the way, it passes through multiple servers that help ensure it arrives at the right place. That email message flow uses a systematic process based on a number of long-established technical standards.
For most users, how an email message flows from the sender to a recipient’s inbox is something that happens behind the scenes. When an individual or an organization sends an email, the message travels from its point of origination, such as an email client where it was composed, across the Internet to its destination. Along the way, it passes through multiple servers that help ensure it arrives at the right place. That email message flow uses a systematic process based on a number of long-established technical standards.
For most users, how an email message flows from the sender to a recipient’s inbox is something that happens behind the scenes. When an individual or an organization sends an email, the message travels from its point of origination, such as an email client where it was composed, across the Internet to its destination. Along the way, it passes through multiple servers that help ensure it arrives at the right place. That email message flow uses a systematic process based on a number of long-established technical standards.
How does an email message flow?
Email has been around since the 1960s, when the creators of nascent computer networks began devising ways to send messages to each other. In those early days, users were limited to communicating only with others on the same shared mainframe system. However, the adoption of standard protocols and the interconnection of systems into the shared network we now know as the Internet allowed different mail systems to “talk” to each other.
It’s these standards that allow us to send email messages to virtually anyone. When someone sends an email message, it flows through a series of steps to reach its destination.
When an individual writes a message, it’s usually done in an email client like Outlook or Apple Mail—or in a web-based service like Gmail.
However, when the message is a transactional email like a shipping notice or a password reset, the message is created automatically by those systems, usually using an email API. (Marketing messages are generated by automated systems as well, although usually in large batches, rather than one at a time like transactional messages.)
In both cases, whether the message is created by an email client or by an automated system, it is specially formatted to be transmitted over the Internet using a standard called “Simple Mail Transfer Protocol” (SMTP).
The sender’s mail server (technically called a “Mail Transfer Agent,” or MTA) looks up the “@domain.com” portion of the recipient’s email address in a Domain Name System (DNS) server to determine which destination mail server (referred to as a “Mail Exchanger,” or MX) it should contact to deliver the message.
The sending and receiving servers communicate using the SMTP protocol. The receiving server accepts the message so that it can be delivered to the recipient.
The recipient’s email client retrieves the message using standards like the Post Office Protocol (POP) or Internet Message Access Protocol (IMAP) to download the message so it can be read.
Email has been around since the 1960s, when the creators of nascent computer networks began devising ways to send messages to each other. In those early days, users were limited to communicating only with others on the same shared mainframe system. However, the adoption of standard protocols and the interconnection of systems into the shared network we now know as the Internet allowed different mail systems to “talk” to each other.
It’s these standards that allow us to send email messages to virtually anyone. When someone sends an email message, it flows through a series of steps to reach its destination.
When an individual writes a message, it’s usually done in an email client like Outlook or Apple Mail—or in a web-based service like Gmail.
However, when the message is a transactional email like a shipping notice or a password reset, the message is created automatically by those systems, usually using an email API. (Marketing messages are generated by automated systems as well, although usually in large batches, rather than one at a time like transactional messages.)
In both cases, whether the message is created by an email client or by an automated system, it is specially formatted to be transmitted over the Internet using a standard called “Simple Mail Transfer Protocol” (SMTP).
The sender’s mail server (technically called a “Mail Transfer Agent,” or MTA) looks up the “@domain.com” portion of the recipient’s email address in a Domain Name System (DNS) server to determine which destination mail server (referred to as a “Mail Exchanger,” or MX) it should contact to deliver the message.
The sending and receiving servers communicate using the SMTP protocol. The receiving server accepts the message so that it can be delivered to the recipient.
The recipient’s email client retrieves the message using standards like the Post Office Protocol (POP) or Internet Message Access Protocol (IMAP) to download the message so it can be read.
Email has been around since the 1960s, when the creators of nascent computer networks began devising ways to send messages to each other. In those early days, users were limited to communicating only with others on the same shared mainframe system. However, the adoption of standard protocols and the interconnection of systems into the shared network we now know as the Internet allowed different mail systems to “talk” to each other.
It’s these standards that allow us to send email messages to virtually anyone. When someone sends an email message, it flows through a series of steps to reach its destination.
When an individual writes a message, it’s usually done in an email client like Outlook or Apple Mail—or in a web-based service like Gmail.
However, when the message is a transactional email like a shipping notice or a password reset, the message is created automatically by those systems, usually using an email API. (Marketing messages are generated by automated systems as well, although usually in large batches, rather than one at a time like transactional messages.)
In both cases, whether the message is created by an email client or by an automated system, it is specially formatted to be transmitted over the Internet using a standard called “Simple Mail Transfer Protocol” (SMTP).
The sender’s mail server (technically called a “Mail Transfer Agent,” or MTA) looks up the “@domain.com” portion of the recipient’s email address in a Domain Name System (DNS) server to determine which destination mail server (referred to as a “Mail Exchanger,” or MX) it should contact to deliver the message.
The sending and receiving servers communicate using the SMTP protocol. The receiving server accepts the message so that it can be delivered to the recipient.
The recipient’s email client retrieves the message using standards like the Post Office Protocol (POP) or Internet Message Access Protocol (IMAP) to download the message so it can be read.
How do email clients download a message?
Web-based email services like Gmail or Hotmail/Outlook.com use their own internal protocols to manage email. But when recipients use a stand-alone email client on a phone or desktop computer, that software uses standard protocols to download messages from mail servers.
When the recipient uses POP, the server delivers all new emails to them and only keeps copies of them if an option in the email client is checked, if applicable. If the server doesn’t have copies of the emails and the recipient suffers a hardware loss or failure, those messages are gone forever, unless the senders have copies of them.
When the recipient uses IMAP, the server syncs the contents of the mailbox, including its Sent Items and other folders, to each device that connects with it. The messages remain on the server, and when the status of one changes (for example, it’s read or deleted), that change propagates across all devices when they connect again.
The ability to retain and sync messages on multiple devices is why most email services today use IMAP instead of POP.
Protocol | How it works | Pros | Cons |
|---|---|---|---|
POP | Downloads emails to one device and optionally deletes them from the server | Simple setup, works offline | No syncing across devices, messages can be lost if the device fails |
IMAP | Syncs mailbox folders and message status across all devices | Consistent experience across devices, messages stored on server, safer | Requires more server storage, depends on Internet connection |
Web-based email services like Gmail or Hotmail/Outlook.com use their own internal protocols to manage email. But when recipients use a stand-alone email client on a phone or desktop computer, that software uses standard protocols to download messages from mail servers.
When the recipient uses POP, the server delivers all new emails to them and only keeps copies of them if an option in the email client is checked, if applicable. If the server doesn’t have copies of the emails and the recipient suffers a hardware loss or failure, those messages are gone forever, unless the senders have copies of them.
When the recipient uses IMAP, the server syncs the contents of the mailbox, including its Sent Items and other folders, to each device that connects with it. The messages remain on the server, and when the status of one changes (for example, it’s read or deleted), that change propagates across all devices when they connect again.
The ability to retain and sync messages on multiple devices is why most email services today use IMAP instead of POP.
Protocol | How it works | Pros | Cons |
|---|---|---|---|
POP | Downloads emails to one device and optionally deletes them from the server | Simple setup, works offline | No syncing across devices, messages can be lost if the device fails |
IMAP | Syncs mailbox folders and message status across all devices | Consistent experience across devices, messages stored on server, safer | Requires more server storage, depends on Internet connection |
Web-based email services like Gmail or Hotmail/Outlook.com use their own internal protocols to manage email. But when recipients use a stand-alone email client on a phone or desktop computer, that software uses standard protocols to download messages from mail servers.
When the recipient uses POP, the server delivers all new emails to them and only keeps copies of them if an option in the email client is checked, if applicable. If the server doesn’t have copies of the emails and the recipient suffers a hardware loss or failure, those messages are gone forever, unless the senders have copies of them.
When the recipient uses IMAP, the server syncs the contents of the mailbox, including its Sent Items and other folders, to each device that connects with it. The messages remain on the server, and when the status of one changes (for example, it’s read or deleted), that change propagates across all devices when they connect again.
The ability to retain and sync messages on multiple devices is why most email services today use IMAP instead of POP.
Protocol | How it works | Pros | Cons |
|---|---|---|---|
POP | Downloads emails to one device and optionally deletes them from the server | Simple setup, works offline | No syncing across devices, messages can be lost if the device fails |
IMAP | Syncs mailbox folders and message status across all devices | Consistent experience across devices, messages stored on server, safer | Requires more server storage, depends on Internet connection |
Read more about email message flow
Email involves many different steps and systems. You can learn more about the inner workings of email delivery with these resources:
Email: This Wikipedia article delves into the history of email as well as its many technical details. It links out to several supporting articles that flesh out the main subject.
Email API: Learn more about how e-commerce and other systems can generate transactional email very efficiently.
Cloud Email Delivery: Learn more about how systems the SparkPost email delivery service work to make large-scale email transmission and delivery practical.
Email involves many different steps and systems. You can learn more about the inner workings of email delivery with these resources:
Email: This Wikipedia article delves into the history of email as well as its many technical details. It links out to several supporting articles that flesh out the main subject.
Email API: Learn more about how e-commerce and other systems can generate transactional email very efficiently.
Cloud Email Delivery: Learn more about how systems the SparkPost email delivery service work to make large-scale email transmission and delivery practical.
Email involves many different steps and systems. You can learn more about the inner workings of email delivery with these resources:
Email: This Wikipedia article delves into the history of email as well as its many technical details. It links out to several supporting articles that flesh out the main subject.
Email API: Learn more about how e-commerce and other systems can generate transactional email very efficiently.
Cloud Email Delivery: Learn more about how systems the SparkPost email delivery service work to make large-scale email transmission and delivery practical.
Join our Newsletter.
Stay up to date with Bird through weekly updates to your inbox.
By submitting, you agree Bird may contact you about our products and services.
You can unsubscribe anytime. See Bird's Privacy Statement for details on data processing.
Join our Newsletter.
Stay up to date with Bird through weekly updates to your inbox.
By submitting, you agree Bird may contact you about our products and services.
You can unsubscribe anytime. See Bird's Privacy Statement for details on data processing.
Join our Newsletter.
Stay up to date with Bird through weekly updates to your inbox.
By submitting, you agree Bird may contact you about our products and services.
You can unsubscribe anytime. See Bird's Privacy Statement for details on data processing.
