Reasons Why Email Delays Occur
Frequently asked support queries revolve around the delay in receiving certain emails, where they arrive hours after being sent. Another common inquiry is regarding the inconsistency in email delivery, specifically when emails sent at 1:00 PM are received after those sent at 1:15 PM, with a delay of approximately 30 minutes.
There are numerous factors involved in the processing of email that may impact its sending and receiving. Generally speaking, emails are typically sent and received instantaneously (within seconds). However, it is not unusual for emails to take anywhere from 15 to 30 minutes to complete the delivery process. In extremely rare instances, emails may experience delays of 24 hours or even up to 72 hours before being successfully delivered or received.
The most common cause is the send/receive cycle of the e-mail program
Companies that provide internet services, as well as email services that are accessed through a web browser. Numerous email programs and services have predetermined intervals for sending and receiving messages. These intervals typically range from a few seconds to 15 minutes. However, users have the option to adjust these intervals to shorter duration in the settings of most email programs or services.
The second most common cause for longer than expected delivery times is Anti-Virus/Spam screening programs
For the most part these programs are quick and usually only delay from a few seconds to a minute, however it is common depending on application for this process to take longer, as e-mails are screened in the order they are received and the over-all file size or attachments can cause delays.
Delays ranging from a few minutes to several hours are typically caused by problems with the network or the Internet. There are many factors at play, but the most common cause is email spooling. When there is an issue with connecting to the internet or when there is a high volume of email to process, an email server may store the emails for a period of time, from a few minutes up to 72 hours. Once the issue is resolved or the service is restored, the email server starts sending out the stored emails, but it gives priority to normal traffic first. Meanwhile, the regular flow of current emails continues, and the stored emails are released when the traffic allows.
An illustration could be rush hour congestion where each car represents an email. You and a colleague both reside on the same street. You depart from work at 5:00, while your co-worker leaves at 5:15. Unfortunately, there is a collision on the freeway causing traffic to come to a halt. As you are stuck in the traffic, you hear the radio station report the accident at 5:05. Your co-worker hears this as well and decides to take an alternative route, bypassing the accident and arriving home 10 minutes earlier than you. The concept of spooling can be further clarified by drawing a comparison to the different lanes of traffic. The accident was in the right hand lane which has caused you to stop. You have to wait to move to the left lane as traffic will allow. This may also allow you co-worker who may have left minutes after you to pass you by and get home 10 minutes before you.
E-mails should rarely take extended times from sender to recipient, but should be expected from time to time. If this issue is common or persists and the majority of e-mails are taking longer than 15 minutes to complete delivery there may be an issue and should be reported. Note the default setting for automatic send and receive with most client servers and e-mail applications is 15 minutes, so unless the user is clicking the send and receive button there is a delay of 15 minutes.