Email delays occur occasionally and the reasons why

Common questions I get for support is why do some emails take longer to receive, hours after they were sent, or Why do some emails get delivered out of order being an email sent at 1:00 PM is received after an email sent at 1:15 PM by 30 minutes or so.

There are many variables in the handling of e-mail that could affect sending and receiving. The average e-mail for the most part is sent and received immediately (within seconds), however it is not uncommon for e-mails to take 15 to 30 minutes to complete the delivery cycle. In very rare cases e-mails can be delayed 24 and up to 72 hours before being delivered/received.

The most common cause is the send/receive cycle of the e-mail program

Internet Service Providers, and or web based e-mail services. Many e-mail programs and services have timed interval cycles for sending/receiving. The most common cycles are from a few seconds to 15 minutes. This can be changed to shorter times in most e-mail programs or services property settings.

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.

The delays of several minutes to hours are usually related to network and or Internet issues. The number of variables are numerous to list here, but typically are related to e-mail spooling. An e-mail server may spool e-mail for several minutes and up to 72 hours, if there is an issue connecting to the internet or processing a large volume of e-mail due to high demand and traffic. When issue is corrected or service is restored the e-mail server starts sending out spooled e-mail, but priority is given to normal traffic first. In any case the normal (current) e-mail traffic flow continues and the spooled e-mails are released when the traffic allows.

An example would be rush hour traffic with each vehicle representing an e-mail message. You and a co-worker live on the same street. You leave work at 5:00 and your coworker leaves at 5:15 while on the freeway there is an accident and traffic comes to a crawl. You are caught in the traffic as you hear the radio station announce the accident at 5:05. Your co-worker hears this and takes an alternate route by passing around the accident and getting home 10 minutes before you. Spooling can be further explained by comparing the traffic lanes. 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.

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