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Why Does Email Take So Long to Arrive Sometimes?

It’s usually quick, right?

Delayed EMail
Counting on email being almost instant is probably a bad idea. Email is designed to tolerate many delays, and delays do happen.
Question: When someone sends me an email, I don’t get it right away. Sometimes it takes hours. It is time-stamped hours before I actually get the message. Could it be because my inbox is too full?

We’re all so used to email being almost instantaneous that we notice delays.

Delays can happen for many reasons, and counting on email to be nearly instant turns out to be a bad idea. You can’t always rely on the timestamp to be accurate, either.

Let’s look at exactly why an email takes a little longer than expected.

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Why does email take so long?

Email was never designed to be instant, and was built with tolerance for lengthy delays. The email infrastructure has improved to the point that it’s almost always very fast, but delays can still happen. Delays are most commonly caused by Server issues and floods of spam.

Server to server

While it seems email goes directly from your outbox to your recipient’s inbox, in reality, it travels across multiple servers. The sender’s email server, and yours, of course; but it’s possible that several intermediate servers may also be involved, each one receiving and then passing the email on to the next server along the route.

Surprisingly, there’s no requirement that those servers operate quickly, or in any timely fashion. In fact, if they’re overloaded with mail, spam, or other tasks, they could take a while, and that’s quite OK according to email protocols.

I would guess that in most cases, delayed email is due to one of the mail servers along the way being overloaded and running slowly. Most often, that’s due to a flood of spam. Naturally, there are other potential causes for delays, including how often you check your mail.1 Delays may be minutes, hours, or, in worst-case scenarios, even days.

And all those delays are OK, at least as far as the servers are concerned.

Delays versus bounces

A full mailbox is typically not a reason for a delay.

If your mailbox is full, most email services return a message to the sender — called a “bounce” — indicating your message could not be delivered. On rare occasions, it might be discarded.

On getting the bounce notification, the sender could try again, and if you’d made room in your mailbox since the first attempt, the mail might be delivered as expected. Depending on how long all that took, it could look like a delay, but it definitely wasn’t automatic. The sender had to take steps to re-send the mail.

Tracing time

One thing making things very confusing is that the date and time displayed on the email are usually the date and time the email was sent, as displayed from the sender’s computer. If they have their date and time set wrong, that wrong date and time shows up on the email they send.

If you’ve ever seen email (particularly spam) “from the future”, that’s probably what’s happened. The clock on the computer sending the email was set incorrectly.

If you examine the mail headers of a message,2 you can see the date and time that each mail server along the way acted on the message. The header will have a series of lines that look similar to this:

Received: from ([]:56405
  by with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.88)
  ...; Thu, 16 Mar 2017 08:16:22 -0700
Received: from ( []) by
  with ESMTP id 8njXs1vAjrlP3xsh (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO)
  ...>; Thu, 16 Mar 2017 08:15:11 -0700 (PDT)

Starting at the bottom and working upwards, you can see the email message make its way from my email service provider ( to a spam-filtering service, and then on to my server ( Each “hop”, as they’re called, includes the timestamp the message was received, which I’ve highlighted in bold above. Note that each timestamp is in 24-hour notation, and also includes its time zone designation. In that last entry, for example, “08:15:11 -0700” indicates 8:15 am in the time zone 7 hours behind UTC (Universal Time Coordinated or, less correctly, GMT, Greenwich Mean Time).

In theory, once you account for time zones, you can relatively accurately trace how long the mail spent on each server along the way, and thus identify any potential bottlenecks. In the example above, the message spent over a full minute on the spam filtering service’s server before being passed to my server.

However, this has one interesting flaw: it still assumes everyone’s clock is set correctly, including all the mail servers. In most cases, they are fairly accurate (at least to within a few seconds), but it’s definitely not foolproof.

Resiliency versus speed

Email is one of the oldest services on the internet, and was designed at a time when computers were not always connected.

As a result, email services, servers, and protocols all have a high degree of resiliency built in. Depending on the type of failure a mail server encounters when attempting to deliver an email, it may elect to reject and return a bounce message, or it may decide to hold on to the message and try again later. In the latter case, it can keep trying for multiple days before finally giving up.

If something you sent or are expecting hasn’t arrived in what you’d consider a reasonable amount of time, check to make sure the message was sent properly. Check the recipient’s spam folder. If you don’t find it, then consider sending it again, using a different provider or a more immediate tool for the job, like instant messaging.

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Footnotes & References

1: It’s less common than it once was, but the act of checking for email frequently could impact the server, preventing it from actually processing email.

2: Unfortunately, exactly how you do this varies based on what email program or interface you’re using. When displaying a single message, look for options referencing headers, message source, or original.

19 comments on “Why Does Email Take So Long to Arrive Sometimes?”

  1. I met an american couple in Feb 2009 in Venice and I exchanged contact details with them. Shortly afterwards I sent them an email to which I never received a reply until now (March 2010). Without going into too much detail, he replied as if I’d just sent it which I thought was strange and when I queried why he was only now getting in touch he replied the email had just arrived and he’d replied as soon as he’d received it. I want to know how it is possible for an email to take more than a year to reach it’s recipient? In the original email I sent I there was a photograph and a link to an online documentary that was quite politically sensitive. Could that have been the reason for the delay? I am in the UK and the recipients live in the USA.
    It would be great if you could shed some light on this. Thanks.

    • I have also had people receive some email from me that were dated over a year old…a couple had events with dates right in the email which proved they were older than a year.

      • I’ve had that happen only to finally discover that it was because I didn’t actually send the email. It sat in my draft folder forever, and then something that I did sent it.

    • I received an email from a lady friend describing what she would be wearing, so that I would recognize her when she arrived for dinner for our first date. I wondered why, because we had been dating for 9 months. I finally looked, and sure enough, it was dated 9 months ago!

  2. I would like to know why it takes so long to get an email from my husband that is in the next room. I don’t get them sometimes until the next day.

    Basically the article you just commented on has that answer. Just because you’re in the next room doesn’t mean anything. The email you send still goes to your email provider (wherever they are), then to your husband’s email provider (wherever they are) and then finally to your hiusband’s computer.


    • Early in the internet email era for non-government/student users, I looked at the headers on some of the messages and found that almost all were hitting servers on universities on both coasts. I was amazed at how fast they got thru.
      I was also on a BBS (bulletin board system) that passed emails through a central hub overnight. When Desert Storm was starting, they set up a node with access to military mail over there. Just put the soldier’s address at the top of the message and they would print it and drop it in the mail to them. My younger brother was amazed at how fast it got to him.

  3. Often when sending has been delayed for a long enough period of time, the sender will receive a delayed delivery warning. In that case, I always resend the email, possibly with an explanation that it is a resend. In the extremely vast majority of cases the resent email will get delivered almost instantly (as the extremely vast majority of emails do). The delayed email will almost surely take a few hours or in many cases bounce.

    And maybe if an email is urgent enough, you might consider sending it twice, possibly from different accounts. It might sound crazy, but we’ve gotten a couple of questions from people who’ve sent out urgent emails which were delayed and eventually bounced.

  4. I’m sending emails to a dear friend whose husband is ill. Two replies were returned from her without messages.
    Would there be a technical reason for this. They seemed to have been delivered and it appears she returned the email.
    There’s no personal reason why there’d be no message.

    • This happens regularly in tech support – receiving tons of this kind of email. I can only guess but I think what happens is that they are getting their email on a phone and they accidentally click the wrong thing and it replies. That can even happen on a computer. So I just call it a “typo.”

    • If by “returned” you actually mean “replied” with no message, I’ve seen this too. I chalk it up to a typo on the recipient’s part. I know of no reason this would happen automatically.

      If by “returned” you actually mean “bounced”, as in an error, then there would be a message there.

  5. I have a gmail account that I have been using for business related communication. I’ve been using it for many months (without issue, as far as I know). Then I started having some doubts and sent multiple test emails from my yahoo account to my gmail account. Most got through…but one didn’t (sent about 8 hours ago). According to yahoo, it’s been sent (it’s in the sent folder). No sign of it on gmail – it’s not in spam, trash, etc. I have no filters, muted or blocked accounts. I’ll also note that even the test emails that successfully came through normally took several minutes each time, as opposed to seconds.

    My question is: at what point do I give up on this gmail account? Changing my email with so many people would be awkward, but at this point I lack confidence in the system. On the other hand, the problem could be yahoo…or something else entirely. No idea, really.

    I know it’s a matter of opinion, but any suggestions on how to approach this? When does a system no longer deserve your confidence? It’s really started to worry me, and I’d appreciate any opinion offered.

    • I certainly wouldn’t give up on it because of one missed email. Spam filters are tricky at best. And the email system is strange. You may find the email arriving later. If you DO change, I’d purchase a domain (as I have,, and then use that as your email address, but routing it through gmail (or or yahoo) or just going direct. That way you can change the “back end” provider at will without changing your email address. All email I get actually goes through a gmail account.

    • When you have any indication that the delivery is being held up, resend the email. It’s better to send two and have them both get delivered than to risk too long a delay or even a failed send. You can inform the recipient, so they understand why they are receiving the same email twice.

    • Shouldn’t. Generally email is close to instantaneous if everything is working. As the article outlines, though, there are other reasons email can be delayed. Surprisingly distance is rarely one of them.

  6. I want to win a contest! My email needs to be the first to arrive. It will have a small attachment (193kb).
    I use Safari and have a gmail extension.
    I have an iPhone, iPad and MAC.

    What could be the fastest way to send to win?…

  7. I can’t understand why the SMTP protocol can’t be updated to send consistently instantaneously. I use a few messaging apps and they are all instantaneous. They are even called instant messaging. Unless the email is business or work related, I use a messaging app. And I use Whatsapp for some work-related messages.

  8. It’s frustrating how many companies behave as though email delivery is instantaneous. So many important accounts can’t be accessed until you “verify your identity” by entering a code emailed to you. But, often, by the time you receive this code, it’s already expired.


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