Dispatching an email does not guarantee reception. When an email has been sent but not delivered, we speak of email “bounces”. The goal of email marketing is to keep the bounce rate (proportion of bounces in the number of targeted email addresses) as low as possible. However, bounces can have many reasons, which each require a different course of actions.
If a dispatched email cannot be delivered, it is called a bounce. Preventing bounces is an important task in email marketing. However, to efficiently take action against bounces, you must know their potential causes. The reasons for bounces are manifold and not each bounce requires action.

1. Inbox Full

When a recipient’s inbox is full, no further emails can be delivered. The bounce message in this case contains a line, such as recipient’s inbox is full. All relevant email clients notify their user, when the inbox is full. As soon as the recipient clears his inbox, the bounce reason is removed and the email can be delivered. Temporary bounces are often called soft bounces. When an inbox is too full over a longer time period, you can assume that the account is no longer used. If emails permanently cannot be delivered, we are speaking of hard bounces. In this case, the recipient should be deleted from the mailing list.

2. Absence

If a recipient is absent for a longer period, e.g. due to illness, he can configure the email out-of-office assistant so that incoming emails will not be delivered. In most cases, this should be obvious from the automatically sent absence message. The cause for the bounce usually corrects itself when the recipient returns, i.e. the out-of-office assistant is deactivated.

3. Email Loop

The email loop can best be explained by means of an example. Let’s assume that a recipient goes on holiday and configures his absence assistant to forward emails to another recipient. This recipient, however, is also absent and has set his absence assistant forwards to the first recipient. The created loop will continuously send emails from one inbox to the other. Most email servers however, are able to identify an email loop and interrupt it  as long as they are correctly configured. A possible bounce message for an email loop would be mail loop: too many hops (too many ‘Received:’ header fields).

4. Address Does Not Exist

Emails can only be delivered to addresses which exist. A bounce due to a non-existent address can be identified, for example through a line, such as “recipient email address unknown”. In this case, you should check, whether the email address has been correctly entered into the mailing list. If addresses were manually captured, there could be a typo. If the recipient himself has made a mistake, e.g. “John.Smiht@xyz.cim instead of John.Smith@xyz.com” you cannot correct the address yourself. When an address does not exist (anymore), you can delete it from the mailing list.

5. Email Has Been Filtered

There is the possibility that an email has been filtered by the recipient’s email server. This can have different causes, which unfortunately, are not always obvious from the bounce message. The most common cause is that the email has been classified as SPAM and the possible message would read: “Email was identified as spam”.

6. Problems With The Email Server

Messages such as error writing message or message could not be stored indicate a fault with the recipient’s email server.