There are multiple factors which affect whether a sent email is received by the recipient. This article explores the options for diagnosing delivery issues.
Sending an email is an exchange between the sender's mail server and the recipient's mail server. The sender's mail server connects to the recipient's mail server, transfers the contents of the email, then the recipient's mail server returns a response code to the sender's mail server advising whether delivery was successful or not.
Check whether the recipient is subscribed
Emails will only be sent to people who are subscribed. Although it might seem obvious, if someone isn't receiving the newsletter, first check whether they are listed as Subscribed on the Email Subscribers page.
If they show as Unsubscribed or Blocked, they won't be sent any emails.
Unsubscribed means they (or you) intentionally removed them from the subscription list.
Blocked means the most recent attempt to send email to them failed (hard bounced). When an email hard bounces, it is automatically blocked from future attempts. You can subscribe them again a limited number of times.
Check the stats
Check the email stats for your most recent newsletters to see whether the email address is a successful delivery or failed delivery.
Sent
If the email address is in the Sent list, this means delivery was successful. Their mail server returned a success response code when our mail server delivered email to them. This means the delivery issue is on their side.
Here are some common issues on the recipient's side:
Email is arriving in their junk folder. Check the junk folder.
A rule is moving email to another folder. Do an entire mailbox search to try and find the email.
[email protected] is on their blocked sender's list. Check the blocked sender's list and remove [email protected]
A corporate email filtering appliance is applying it's own filtering logic and blocking the email before it reaches the recipient's mailbox. The recipient will need to ask their IT department to check for blocked emails and allow them through
Note that corporate mail servers will sometimes block the email internally, but return a success response code to our mail server. Although this is non-standard behaviour, it is unfortunately common and we can only rely on the response code provided by the recipient's mail server as to whether delivery succeeded or not.
Failed
If the email address is in the Failed list, this means the recipient's mail server returned a error response code when our mail server delivered email to them, or the recipient's mail server couldn't be contacted. There will usually be a reason (which the recipient's mail server provided along with the error code).