Joran Hofman
April 4, 2021

What is email Delivery?

This occurs when an email is sent to a receiving mail server using SMTP (Simple Mail Transfer Protocol). The receiving mail server then decides whether or not to accept the message. "Delivery" refers to the acceptance or not of the message by the server.

This occurs before the message is placed in the inbox or spam folder.

Why is Delivery important?

Email delivery is extremely important, especially when the emails sent are vital in importance to the company, such as the return of keys or passwords, status notices, and impending alarms. This is because if the emails land in the spam or junk mail folder, they will be of no use to either the customers or the person who sent them.

How does email Delivery work, and when is a message considered delivered?

To answer the question of when an email is considered "delivered", there are several different answers. Here are three of the most common answers to this question.

 An email is considered to have been delivered when:

  • The receiving email server accepts the sent email: The message originating from the email client of the one who sends it, and the receiving email server receives it without problems. However, the receiving mail server still has a lot of work to do in deciding how to best handle the message. 

This can be compared to sending an envelope or package to the package receiving room of a building with multiple departments and offices. In the reception room, surely a person signs that the package was received, but this does not mean that the person to whom it was sent received it.

  • The message is placed in the corresponding mailbox on the receiving mail server: in this case, the message, in addition to being received by the mail server, was also placed in the corresponding mailbox. 

Utilizing the example mentioned above, this would be like sending an envelope or package to a package receiving room, ensuring that someone signs the package, and then delivering the package to the person it was sent to. Whether or not the person opens the package is not taken into account here.

  • The final recipient opens and reads the sent message: finally, in this case, the question is fully answered by stating that the final recipient received, opened, and read the message.

As seen in the 3 cases mentioned, the meaning of "delivered" changes according to the context, the email service provider, and the current situation, and all three answers would be correct. But from a technical point of view, there is only one correct answer.

250 OK Status: to be sure that an email was delivered or not, from a technical point of view, a message is considered delivered when the sending mail server receives an SMTP response "250 OK" when an SMTP transmission is concluded.

What does the "250 OK" status mean?

A response message from the server of "250 OK" means that the SMTP communication was successful and is relayed in response to every supported command, possibly 4-6 times for each message.

The person sending the email will seldom notice the response “250 OK, as this code is displayed in the background after an SMTP email delivery broadcast. So a message can be considered delivered when it reaches the destination inbox.

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