In an emailing campaign, it often happens that the sent messages come back to their recipient. A case little appreciated by the experts of emailing. Our question of the day is therefore: Why some emails do not reach the targeted inbox and come back to the sender?

We explain the possible causes and how to solve this problem.

The bounce

In emailing, we talk about bounce to designate an email that could not arrive at the recipient. There are two different types of bounces:


The soft bounces

The bounce is a temporary problem that prevents your email from being delivered to an address for various punctual reasons:

  • Storage limit reached by the recipient’s inbox, so impossibility to receive any new email. Attention, if that persists, the user may simply only use this account, making the address nonexistent (Hard Bounce).
  • Server momentarily unavailable (here too it can turn into hard bounce if the problem persists)
  • Email sent too large
  • Email of the sender placed on gray list, or temporarily refused

Recall that in the case of Soft Bounce, the problem is temporary. No sentence, so immediately remove the addresses indicating a soft bounce. The server will usually continue to send the email until it finally reaches its destination. However, if the problem does not adjust, it may be necessary to delete the address in question from your list so that it does not lead to Hard Bounce.


Hard Bounce

More problematic than the soft bounce, the Hard Bounce is permanent in the sense that the address you are trying to send the message no longer works. This can be explained by several reasons:

  • Email address no longer existing
  • Bad Email Entry (fault in the address)
  • Email address of the sender blocked by the recipient (in this case, check the reasons to make sure you are not on blacklist or considered as spam)
  • Server failure
  • Bad configuration of the recipient’s inbox

In the case of an invalid / non-existent address, unless you find a way to process the error, do not take a risk by insisting and delete it immediately from your list to avoid any problem.


How to prevent your emails sent back as non-deliverable?

mail delivery failed
Although each campaign emailing has its lot of non-deliverables, it is possible to keep the bounce rate at its minimum by following some instructions:

  • Clean your lists regularly.
  • Flee at all costs Lists for rent or buy.
  • Take the time to build healthy lists with valid addresses, including using the opt-in or the double opt-in in your registration forms.
  • Build your message correctly so that it is not considered spam (words, formulations, layout, etc.).
  • Check the validity of the receipt boxes of your recipients via the protocol SMTP.
  • Set up a regular shipping schedule to prevent your emails from being taken for spam.

Whether its simple bounce or hard bounce, you should automatically receive a specific error code regarding the nature of the problem. This precision will allow you to process each return on a case by case (a soft bounce will not be solved in the same way as a hard bounce).

Finally, remember that any campaign displays a bounce rate, no need to panic to the slightest email returning as not delivered. However, the higher this rate, the more negative impact your reputation as sender as well as the delivery of your email. Hence, the importance of following the basic tips above, in order to avoid bounced hard and keep the bounce percentage at its minimum.