Soft vs Hard Email Bounces


When an email is not deliverable to the intended recipient, it is commonly known as a “bounce”. In a case like this, the receiving mail server will send a notification back to the sender address to inform them that the email has not been delivered. A bounce notification will include a reason for the bounce, which generally falls into two broad categories: “Hard” and “Soft” bounces. Here is a look at Soft vs Hard email bounces:

Hard bounces

A hard bounce is a mail that’s considered ‘permanently undeliverable’. Hard bounces are often caused by sending emails to unknown or non-existent domains, which generally result from questionable data sources or spam, and can cause an email address to be blacklisted. A hard bounce can often happen when implementing reactivation campaigns, where brands try to re-engage dormant or low-engagement users. There are a few ways in which this can happen but, most commonly, hard bounces happen when:

  • Sending to inactive and non-existent email addresses,
  • Non-existent domain names or
  • When there is blocked delivery by a recipient email server.

As a general rule of thumb, receiving over 30% hard bounces is a major cause for concern - this usually only happens on list reactivation campaigns, or is more than likely a spammer. In these cases blacklisting is very possible. A 5-10% hard bounce rate is quite common for single opt in lists, including a higher chance of spam traps. 1% or less hard bounces on the other hand, is usually to be expected with databases that are double opt in.

At TotalSend, hard bounced email addresses are automatically added to a Global Suppression List, which is a digital documentation of suppressed email addresses that exists in accordance with the CAN-Spam Act of 2013.

Soft bounces

A soft bounce is a mail that is considered temporarily undeliverable where the server rejects the email due to seemingly temporary conditions. Three to five attempts at sending are usually made before the email is considered to have hard bounced. There are a few reasons why a soft bounce can occur, the most common of these are:

  • Recipients mailbox is temporarily full
  • There is a temporary domain failure
  • The account is disabled or inactive.

However, soft bounces can also be the result of block bounces, where the email server rejects the email due to filtering issues, such as:

Other technical reasons for soft bounces could include a busy server or a data format error. It is also possible that a network error has occurred.

What can you do to prevent and treat bounces?

Remember when considering soft vs hard email bounces, soft bounces are expected in small quantities and not necessarily a reason to panic, however, hard bounces can become a much bigger problem if they become a regular occurrence. Regular list maintenance and testing is a good start when it comes to minimizing your bounce rate. Make sure that you are:

  • Avoid sending to old or out dated lists by maintaining your e-mail list “hygiene” can reduce e-mail bounces. Find out how and why to stick to list best practices here. For ways to building and maintaining a healthy subscriber list, click here.
  • Using double opt in forms. This requires your subscribers to confirm their subscription, but is a fantastic way to ensure that they’re keen to hear from you and are more likely to engage with your mails. Recipients will receive a “Welcome” mail, asking them to confirm their subscription by clicking on a confirmation link. Once this is confirmed, you can then decide whether or not you’d like to send a final “Thank you” mail.
  • Testing your email messages regularly is a great way to measure results. According to Comms100, best practice for testing your emails involve segmenting your lists by demographics and customer behaviour, and measuring results regularly to support your approach or to highlight where changes still need to be made.They also suggest removing your most inactive and most active users from the testing pool. The “most active” could simply be people who've opened a mail from you in the last month or two, while the most inactive may have only opened one 12 months ago.
  • Monitoring your email delivery. Focus on how many people are marking your emails as spam. If it’s more than 0.3% a month it is considered problematic. She also suggests monitoring how many mails are being delivered and opened in order to help you adjust your strategy accordingly.

This will assist you to gain credibility as a sender and help ensure that your database remains engaged and active for a rewarding campaign, devoid of excessive mail bounces. It’s best to partner with a professional ESP that can adapt your lists and strategy accordingly.