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Why do Emails Bounce?

After creating a contact list for your email marketing campaign, even with the most up-to-date email addresses that you know are valid, you can expect to receive a few bounce-backs. So why does this happen?

When you send an email, the receiving mail server uses an MTA (Mail Transfer Agent) to deal with incoming mail and its deliverability. If there is a mistake in the email address you sent to or an issue with the recipient’s mail server, the MTA will relay a bounce-back message to inform you that there was an error in delivering your email.

An email that bounces, also known as an undeliverable email or a bounce-back, is an email that never reaches its intended destination. This is a common issue for email marketers who send to large lists of email addresses, and there are a few reasons as to why this occurs.

The different reasons an email can bounce are:

  • An email address may no longer be valid or active, e.g. if an employee has left a company.
  • An email address may have never existed, e.g. someone may have supplied a false email address or it features a typo.
  • The recipient’s mail server is experiencing issues when your message is sent.
  • The recipient has a full mailbox.
  • The email was blocked by the recipient’s email server firewall or spam filter.
  • The recipient has an auto-reply set up, such as an out-of-office.
  • The email message was too large.

These types of bounce-backs fall into two categories: soft bounces and hard bounces.

A soft bounce indicates a temporary delivery issue with the recipient’s address. This typically happens when an issue has occurred with the recipient’s email server, the recipient’s mailbox is too full or your email message is too large. With a soft bounce, if you try to resend the email at a later date, it is likely to deliver.

A hard bounce, however, is a permanent problem. For example, the recipient’s email address no longer exists, or your email has been blocked by the recipient’s email server. When you experience a hard bounce, you should not attempt to resend the email as it will never be delivered.

What to do about bounce-backs

As previously mentioned, if you experience a soft bounce, you can attempt to resend the email. However, if you keep receiving soft bounces from the same address, you should assume the address is no longer in use.

For hard bounce emails, you should immediately remove the address from your list. However, make sure to check if there are any obvious spelling errors in the email address before deleting it.

If you use a third-party email marketing service to send mass marketing emails, then all hard bounced emails should automatically be removed by the service. Soft bounced emails will also be removed after a few failed attempts.

It is good practice to cleanse your email lists frequently to avoid experiencing any bounce-backs. This will help you save money especially if you use email marketing services that charge per address sent.