FAQ & Interesting facts

What is a bounce?

A „bounce“ is an error message automatically generated by the email server when an email could not be delivered. It is divided into two categories – soft bounce and hard bounce. A soft bounce is the result of a temporary error, e.g.: the recipient’s mailbox is currently full. As soon as they clear it out, emails can again be delivered. A hard bounce is the result of a permanent error, e.g.: the user no longer exists, or the recipient has left the company.

How is bounce information transmitted?

Standard users know a bounce as an email landing in their inbox. However, there is generally no email coming back from the recipient’s side: it is generated by your own mail server. Only in about 25% of cases is an actual email sent back from the other server. In the case of a temporary error (soft bounce), the originating server will try delivering the email several times. Only after X attempts will the process be aborted and a bounce email generated.

What kinds of errors can occur when sending?

  • Greylist – the recipient email server initially rejects the email and only accepts it after a delay.
  • The email contains words which have been highlighted as potential spam.
  • A domain in the email or the originating IP address appear on a blacklist.
  • The recipient email server has a technical problem.
  • Too many connections, hard drive full, etc.

What are the benefits of an Email Relay Service?

An Email Relay Service has access to the bounce information relayed in the process and can format this and make it available as JSON. Additionally, it automatically categorizes the bounce information (hardbounce, softbounce, greylist, etc.). This allows you to inform a customer who uses greylist that their email has been delayed but will be delivered shortly – e.g. when someone is waiting for a registration email. In addition to this info, there is an automatic delivery confirmation when the email has been successfully passed to the recipient’s mail server.