What are hard and soft email bounces

If you have an active campaign, you might receive an email notification about undelivered campaign emails. These undelivered emails are bounces. A bounced email is an email that can’t be delivered because of a server mistake. There are of two types of email bounces – hard and soft.

Read the bounced email report carefully to find out the exact reason why an email bounced. This will help you make a decision on whether you should keep sending your campaign to the bounced email address.

Hard bounce

A hard bounce is when an email is returned to the sender because the recipient’s email address is invalid. It indicates a permanent reason why an email wasn’t delivered.

A hard bounce can occur when:

  • there is a typo in the email address
  • the email address doesn’t exist at all, i.e. it’s invalid
  • the email address doesn’t exist anymore (for example, because the person has left the company)
  • the domain name doesn’t exist
  • the recipient’s email server was blocked
  • the sender’s email address has received too many soft bounces

Sometimes you might get too many hard bounces because you have not verified your list before sending. Verify your email list and decide whether you’ll be sending the campaign to that address depending on the email’s status.

Note: the higher the bounce rate, the more likely the sender is to be blocked by the ESP.

Soft bounce

A soft bounce is when an email is returned to the sender because an email address is temporarily unavailable.

An email returns as a soft bounce if:

  • the email size is too large
  • the recipient’s inbox is overfilled
  • the recipient’s server is down or temporarily offline
  • emails from the sender have been marked as spam by multiple recipients
  • the sender was blocked for being blacklisted
  • the sender’s email address (or the domain name) was blocked by the recipient’s server (or the recipient)

In the case of a soft bounce, you can send emails to the recipient again, but you will need to resolve the issue causing the bounce first. Often, you just need to wait and try again later.

If you suspect soft bounces are caused by email rejections and blocks, the reasons may be that:

  • you send bulk emails from a free account, for example, a @gmail.com address (Gmail has spam restriction guidelines) causing a message block
  • the recipient’s server believes the email you’ve sent is spam causing SMTP Rejection/Error 554
  • the sender’s email address or IP is on the spam list, resulting in SMTP Rejection/Error 554

You can try solving each issue individually and sending the emails again.

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