Sending emails is a common requirement for many modern applications and enterprises. Use MailSlurp's free email API to validate email addresses in code or using an online dashboard. See the developer email validation documentation for more details.
What is an email bounce back?
A bounced email is an email that is returned to the sender by a receiving mailserver that refused or could not process the message. This typically occurs when sending emails to addresses that do not exist or are full. When a mailserver returns many emails to a sender the sender is considered a bad actor and their spam ranking is marked down. Therefore it is important to reduce the bounce rate when sending emails.
What happens when a bounce is received
When sending emails with Mailslurp a
is used that servers can send a bounce back to. When they do MailSlurp records a bounce event against your account. There is a maximum daily bounce rate and a maximum total bounce count that limits your account. Exceeding these limits can result in temporary account freeze.
Managing your bounces
sidebar link to view your account bounces:
Click on a bounce to view the bounce message and diagnose the cause of the rejection. Try to prevent sending to similar addresses or use the validation features to filter out bad email addresses when sending.
Why it is important to check email lists before sending
Bounce reputation and consequences
Too many bounces or complaints from emails sent from your account can lead to sending ability being suspended. If this happens please contact support.
Verify email lists before sending
When sending marketing emails in MailSlurp use the sending validaiton options in the compose screen to verify email addresses during sending using the MailSlurp web app dashboard.
You can also enable filtered of any previously bounced recipients with the check-button below:
Filtering bounced emails will ensure no emails are sent to any addreses that caused a bounce in your account in the past.
How to verify a list of emails
You can also verify emails in the dashboard and view the results online.
Checking email addresses when sending
Combine MailSlurp's powerful email checking algorithms and live SMTP mailserver checks to filter invalid recipients from your emails when sending. See the following email sending example in Java:
Verifying email addresses online in the dashboard.
MailSlurp offers a powerful online dashboard for validating email address and contact lists in bulk. Simple sign up and navigate to the verification section. Enter your addresses separated by a new line and click verify to check each address against remote mail servers to see if they exist and accept mail.
Receive bounce notifications using webhooks
The best way to avoid additional bounces is by creating an account webhook for
events. See the webhook documentation for event descriptions.
With webhooks your server is sent a payload each time a bounce occurs containing the email addresses of bounce recipients. You can save these bounced email addresses to a ban list and avoid sending to them in the future. See the account webhook guide for more information.
What does an SMTP bounce back look like?
A raw multipart MIME message delivered with SMTP can contain multiple parts with different
What is the response format?
Email messages are Mime Message format that is often multi-part. The parts of the SMTP message body are marked with Content-Type headers. RFC6522 describes the delivery of administrator messages. These admin content parts are used to transmit a delivery status notification or undelivered email when a bounce occurs. When the message is returned to the MailSlurp server a header such as below is sought:
Bounce emails returned to the sender normally contain a standard
content part with a message about delivery.
Then after that will sometimes be a
content part with headers in the body that indicate the reporting mail transfer agent (Reporting MTA) and a diagnostic message for the final recipient.
RFC3464 describes the delivery status content part that is included by most mail transfer agents when a bounce is returned to the
Undelivered message (message/rfc822)
The original undelivered message is included in the returned email.
Viewing bounces for your account
You can view and diagnose bounce alert in your account on the bounces page of the app.