Bounces occur when email servers reject messages for various reasons. There are three main categories: Hard Bounces, Soft Bounces, and Blocked Bounces. Below are descriptions of each type and how iPost manages them.
Hard Bounces
There are various reasons as to why an email may hard bounce. The most common reason is that the domain name does not exist or the recipient is unknown. This may be due to misspellings in your address list, to recipients changing email providers, or to businesses closing.
Addresses that hard bounce may be considered bounced-out addresses and emails will not be sent to them again. This is based on the value set under Delivery Management in your General Settings.
Soft Bounces
Soft bounces usually indicate a temporary delivery issue, such as the recipients inbox being full or the receiving email server being down.
Soft bounces are handled differently than hard bounces. When a soft bounce occurs, the system will attempt to resend the same email over a 2-4 day period. If the email continues to soft bounce consistently, it will be counted as one hard bounce after that period.
Blocked Bounces
A block bounce occurs when the email server rejects the email due to filter issues. These issues could include URL blocks, a lack of proper authentication, or blacklisting.
While block bounces are reported as hard bounces in your delivery statistics, they are not handled by your hard bounce settings. This means subscribers will not bounce-out of your mailing audience due to a blocked bounce.
Bounce Message Translation
The table below provides a list of Bounce Codes and additional information, such as bounce descriptions and if delivery retries will be attempted.
| Retry | Bounce Description | SMTP Codes |
|---|---|---|
| Yes |
Temporary failure (soft bounce) |
Temporary failure (soft bounce) |
| No |
Accepted but returned, no reason given |
2xx then 5xx (out of band) |
| No |
Destination system refusing retry attempts |
432 |
| No | Bad destination address | 501, 511, 512 |
| No | Bad destination address syntax | 513 |
| No | Destination mailbox ambiguous | 514 |
| No | Destination mailbox moved | 516 |
| No | Destination mailbox disabled | 521 |
| No |
Message length exceeds administrative limit |
523 |
| No | Destination had error when forwarding | 524 |
| No | Undefined destination system problem | 530 |
| No | Destination mail system full | 531 |
| No | Destination system not accepting messages (possible spam block) | 532 |
| No | Destination system not capable of feature | 533 |
| No | Message too large for destination system | 534 |
| No | Destination configuration error (possible spam filter) | 535 |
| No | Undefined network or routing issue | 540 |
| No | No answer from destination system | 541 |
| No | Bad connection to destination system | 542 |
| No | Directory server failure | 543 |
| No | Unable to route to final destination | 544 |
| No |
Mail system congestion |
545 |
| No | Routing loop detected | 546 |
| No | Destination mailbox unavailable (possible spam filter) | 550 |
| No | Destination mailbox unavailable (address has changed) | 551 |
| No | Relaying denied (possible block) | 553 |
| No | Delivery transaction failed | 554 |
| No | Problem processing message content | 560-569 |
| No | Delivery not authorized (probably spam filter) | 570-579 |
| No | Undefined destination mailbox error | 510, 520 |
| No | Destination mailbox full | 522, 552 |
| No | Retry time expired on temporary failure | 447, 547 |