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What factors could contribute to message delivery delays?


Email delivery delays can occur for many different reasons. Before we discuss the reasons for delays, let’s start by talking about the process of how email is delivered.

Message creation

You create a mailing template and assign that template to a list. Cordial builds the mailing, checks the suppression list, and then hands the messages off to the sending server. Your server continues to deliver the message until it is accepted, bounced, or times-out. A message will time out if the receiving server refuses to accept the message. The point the message expires depends on the aptly named “Time-to-Live” setting. Our default TTL setting is 24 hours.


In a perfect world, every ISP would accept every message within the first few moments. Our servers are set up to deliver the mail as quickly as possible. Most of the mail gets delivered in the first few minutes. Depending on the size of the mailing, and any Cordial platform settings, some messages may take hours to get delivered.

Delivery delays

The main reason for delivery delays is throttling by the ISP. Throttling means the ISP is reducing how many messages they will accept within a time period.

Sometimes, an ISP will accept your mail in just a few minutes, but delay handing those messages to various recipients. When this happens, the time-stamps on the mailing may not match the data in the Cordial platform. Other times, the messages are still on our server hours after the send as we wait for the receiving server to take and deliver the mail.

Reasons for the delay

ISPs consider three main areas when it comes to throttling email delivery: 

1. Authentication

Incorrect or missing DNS records will reduce the ISP's message acceptance rate. It takes longer for the receiving server to validate the messages, so those messages get delivered at a slower rate or not at all.

2. IP reputation

ISPs will limit the number of messages into their network based on the reputation of the IP address and the “from” or “sending” domain. Sender behavior impacts IP reputation if the bulk of your sending goes to bad addresses. Sending too many mailings often reduces open rates, which lowers your IP reputation. Sending to very old addresses will also impose rate limits due to recipient behavior.

3. Recipient behavior

Recipient behavior is what the recipient does with the message once it is received. If the recipient opens/clicks on the mailing, or moves mail from the bulk folder to the inbox, that is considered good behavior. This increases the reputation of the IP, which improves the email volume entering the network. Deleting the mail without reading or clicking on the abuse button would be a bad behavior that decreases sender reputation, which will reduce the volume of email entering the network.

Improve your delivery rates

Improve your delivery rate by improving your IP reputation. You can improve your IP reputation by sending to active opener/clickers, which reduces bad mailbox issues, abuse complaint issues, unopened mail, and bounces. The ISPs are looking at opens when determining the “value” of the mailing. Focusing on engaged recipients shows the mailing is wanted and will increase the number of messages they accept in a minute/hour.

Sending to old inactive addresses generates high abuse complaints, spam trap hits, and reduced opens, all of which make your mailings look less important.

Finally, make sure you are not over-sending. Mailings become stale and recipients stop opening messages. This impacts IP reputation and delays delivery.




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