Email delay can be frustrating. If you're like most people, you probably expect email to be near-instantaneous, and most of the time, it is. But the complexities of modern email systems and anti-spam efforts can sometimes create a delay. While the causes for delay can vary, it usually falls into one of three groups: greylisting, rate limiting, or a temporary issue with your host.
Sometimes email is delayed on purpose to filter out spam based on the behavior of the sending server. This is called greylisting. During this process, the incoming mail server temporarily rejects a message from a specific sender and asks them to try again. If the email is legitimate, the sending mail server resends the message a few minutes later. The incoming mail server accepts it.
The idea behind this practice is that spammers won't bother to resend bounced messages because they're sending mail to thousands of email addresses each day, but a legitimate sender usually will.
Outgoing email delay caused by greylisting is beyond your control because the receiving mail server is responsible. However, if you suspect your incoming email delay is the result of greylisting, check to see if you have Spam Hammer enabled. Spam Hammer employs greylisting in the fight against spam, and its methods are known to cause a delay in some cases. These delays are usually no more than 15 minutes but can be up to 4 hours.
Rate limits are set to restrict the number of incoming and outgoing emails within a specific time window to limit abuse. Any mail that isn't allowed through is either added to a delivery queue or temporarily rejected. Most hosts have restrictions like this in place to protect their servers from being overwhelmed by accepting and delivering messages. Delays caused by rate limits are usually temporary and resolved on their own. However, some mail hosts employ rate limiting on all inbound emails from other hosts as a way of encouraging users to use their services. If you suspect this is what's happening, contact the mail host for more information.
There are various of reasons why your email may be delayed, most of which are unintentional and will resolve on their own. For example, a problem at the sending or receiving mail server will cause the email queue to build up and result in delay, which will be resolved once the mail server is back online. However, problems like these are usually temporary, so there's nothing to worry about.
To pinpoint the source of the delay, it's essential to analyze the full message header, which contains a detailed log of the network path it took to reach its destination, including how long it was at each location, so you can identify where the delay occurred.
Follow these steps to analyze your email header:
- Open the email you received late, and retrieve its complete message header by following the steps for your mail application in the article Displaying Email Headers.
- Copy the message header in full.
- Now we're going to use an online email header analyzer. Our favorite is MxToolbox, but you can use any of the top results in a Google search. Go to https://mxtoolbox.com and click Analyze Headers in the top menu.
- Paste the message header you just copied into the textbox, and then click the Analyze Header button.
- The contents of the header will be analyzed and translated into a table that lists how long the message was spent at each location. Review the information to identify any irregularities.
Now that you know where the delay is coming from, you can take action.