Email bounces
How MailBlastr records hard and soft bounces, and suppresses permanent or repeatedly failing recipients.
A bounce means the receiving mail system rejected your message. MailBlastr distinguishes two kinds, and treats them differently:
| Type | What it means | MailBlastr behavior |
|---|---|---|
| Hard (permanent) | The address is invalid or permanently undeliverable. | Email status → bounced; the recipient is auto-suppressed for your account. |
| Soft (transient) | A temporary problem — full mailbox, throttling, grey-listing. | Recorded as delivery_delayed or bounced; one failure remains retryable, but a second soft bounce within 30 days is auto-suppressed. |
Bounce types and subtypes
When a message bounces, MailBlastr reports a type and a more specific subtype describing why delivery failed. These are recorded on the email so you can tell a permanent failure apart from a retryable one. There are three types:
| Type | Subtype | What it means |
|---|---|---|
Permanent (hard) | General | The recipient’s provider sent a hard bounce — the address is undeliverable and will not accept the message. |
Permanent (hard) | NoEmail | The recipient address could not be extracted from the bounce message. |
Transient (soft) | General | A general temporary failure. A later send to the same recipient may succeed once the issue clears. |
Transient (soft) | MailboxFull | The recipient’s inbox was full. Retrying later may succeed. |
Transient (soft) | MessageTooLarge | The message exceeded the recipient provider’s size limit. Reduce the size and retry. |
Transient (soft) | ContentRejected | The provider rejected the message content. Changing the content may let it through. |
Transient (soft) | AttachmentRejected | An attachment was unacceptable (file type or size). Remove or change it and retry. |
Undetermined | Undetermined | The server bounced but the message lacked enough detail to classify the reason. |
Permanent bounces auto-suppress immediately. A single Transient or Undetermined bounce remains retryable; a second soft bounce for the same address within 30 days auto-suppresses it, preventing a persistent full mailbox or receiver failure from being retried indefinitely. Note that some autoresponders signal as a Transient bounce rather than a real failure.How bounces are recorded
When a bounce is reported, MailBlastr matches it to the original email, advances its status to bounced (or delivery_delayed for a transient delay), and appends a bounced (or delivery_delayed) entry to the email's event log. The same event is forwarded to your webhooks as email.bounced (or email.delivery_delayed). Redelivered notifications are de-duplicated, so a bounce is never recorded or forwarded twice.
Auto-suppression after permanent or repeated failure
A permanent bounce immediately adds the recipient to your account-wide suppression list. A first soft bounce remains retryable, but two distinct soft-bounced emails within 30 days add the address too. On every later send, MailBlastr skips that recipient — protecting your sender reputation without permanently blocking an address for one short-lived outage.