If an e-mail can not be delivered it generates a bounce response.
There are two main bounce types when working with e-mail. We work with soft bounces and hard bounces.
Soft bounces
A soft bounce is a temporary error which happens when delivering an e-mail. A soft bounce may be due to:
- A temporary issue with the receiving mailserver
- A temporary network issue between the sending mailserver and the receiving mailserver
- A recipient having a full inbox, ie. no more space to store new e-mail
- A temporary DNS issue when looking up the domain the e-mail is delivered to
- So-called greylisting – an anti spam meassure
All of these errors will generate a soft bounce. When Heysender receives a soft bounce our mailservers will continue trying to deliver the e-mail for up to 72 hours after the first attempt. The time between each delivery attempt will grow until the server finally gives up delivering the e-mail.
Heysender will let you know using a webhook if delivery failed due to a soft bounce but it may take up to 72 hours for Heysender to send the webhook since this is the time it takes for delivery to finally fail.
Hard bounces
A hard bounce is a permanent error which happens when delivering an e-mail. A hard bounce may be due to:
- A server being permanently down
- An employee no longer being employed by a company and thus the e-mail address is removed
- An e-mail user changing from one e-mail provider to another resulting in the e-mail address being removed
- A permanent DNS issue when looking up the domain the e-mail is delivered to
- The sending e-mail address or IP address being added to a blocklist
All of these errors generate a hard bounce. When Heysender receives a hard bounce we will immediately send a webhook request notifying the sender of the hard bounce. We will also add the recipient to the suppression list meaning that the Heysender user will not be able to send to the e-mail address again.
The Heysender suppression list
A bounce message (both soft and hard) is the only way a receiving mailserver can notify a sending mailserver that a recipient e-mail address does not work and should not be sent to in the future. This is why Heysender has a suppression list – to identify defective e-mail addresses and remove them.
It is in both the sender’s and receiver’s interest to remove defective e-mail addresses. The sender will not spend money and resources on sending e-mail to an e-mail address which does not work or exist and the receiver will not spend resources handling e-mail traffic which will not result in an e-mail being delivered.
Receiving mailservers use the way a sender handles bounce messages to evaluate the quality of the sender. If the sender does not remove defective e-mail addresses this may result in future e-mail from the same sender being seen as spam and marked as such.
To make sure you avoid being seen as a spammer it is very important to remove defective e-mail addresses from your list. The Heysender webhooks and suppression list will help you with this.