Email is delivered and acknowledged by Mail Transfer Agent (MTA) software located at both the sender (BombBomb) and receiver (ISPs). Sometimes, the receiver refuses delivery of the email resulting in a bounce. The receiving MTA effectively 'returns' the email and uses a bounce code to report why. Additionally, sometimes the receiver does not give a reason.
Bounces are either soft or hard. Soft bounces are generally related to the receiver being too busy to handle more email traffic at this time. BombBomb handles these types of bounces automatically by retrying multiple times to deliver the email over a set period of time. If an email soft-bounces too many times, the receiving MTA will eventually send a hard bounce.
BombBomb handles hard bounces by placing those email addresses on the Suppression List. Here is a standard list of bounce codes returned by receiving MTA:
Code Type Description
5.0.0 Hard Address does not exist or email tagged as SPAM
5.1.0 Hard Other address status
5.1.1 Hard Bad destination mailbox address
5.1.2 Hard Bad destination system address
5.1.3 Hard Bad destination mailbox address syntax
5.1.4 Hard Destination mailbox address ambiguous
5.1.5 Hard Destination mailbox address valid
5.1.6 Hard Mailbox has moved
5.1.7 Hard Bad sender's mailbox address syntax
5.1.8 Hard Bad sender's system address
5.2.3 Hard Message length exceeds administrative limit.
5.2.4 Hard Mailing list expansion problem
5.3.0 Hard Other or undefined mail system status
5.3.2 Hard System not accepting network messages
5.3.3 Hard System not capable of selected features
5.3.4 Hard Message too big for system
5.4.0 Hard Other or undefined network or routing status
5.4.1 Hard No answer from host
5.4.2 Hard Bad connection
5.4.3 Hard Routing server failure
5.4.4 Hard Unable to route
5.4.6 Hard Routing loop detected
5.4.7 Hard Delivery time expired
5.5.0 Hard Other or undefined protocol status
5.5.1 Hard Invalid command
5.5.2 Hard Syntax error
5.5.4 Hard Invalid command arguments
5.5.5 Hard Wrong protocol version
5.6.0 Hard Other or undefined media error
5.6.1 Hard Media not supported
5.6.2 Hard Conversion required and prohibited
5.6.3 Hard Conversion required but not supported
5.6.4 Hard Conversion with loss performed
5.6.5 Hard Conversion failed
5.7.0 Hard Other or undefined security status
5.7.1 Hard Delivery not authorized, message refused
5.7.2 Hard Mailing list expansion prohibited
5.7.3 Hard Security conversion required but not possible
5.7.4 Hard Security features not supported
5.7.5 Hard Cryptographic failure
5.7.6 Hard Cryptographic algorithm not supported
5.7.7 Hard Message integrity failure
If you have any questions regarding bounce codes or any delivery issues feel free to reach out to delivery@bombbomb.com