I'm experiencing a higher bounce rate than usual, why is that?
Email addresses found with Zaplify are averaging a bounce rate of 5-10%. Occasionally, however, bounces might come out higher. The reason for that is that while Zaplify is great at sending and analyzing emails, there are still a few "bounce mechanisms" difficult to prevent. Examples of such bounce reasons/mechanisms are:
Spam filters: If the recipient's email server has strict spam filters, the email may be flagged as spam and bounce back to the sender.
Blacklisted sender: If the sender's email server or IP address has been blacklisted, the email may bounce back or be blocked by the recipient's email server.
Attachment size: Some email providers have limits on the size of attachments that can be sent, so if the attachment is too large, the email may bounce back.
Full mailbox: If the recipient's mailbox is full, the email cannot be delivered, and it will bounce back to the sender.
Email server issues: Sometimes, the recipient's email server may be down or experiencing technical difficulties, which can cause the email to bounce back.
What's good to be aware of is that there are two types of bounces: hard bounces and soft bounces. The "hard bounce" is difficult to control due to that it simply occurs because the recipient's email address doesn't exist. But the "soft bounce", you actually can control, and the best part is that this also is the most common type of bounce.
What are soft bounces and how can you avoid them?
A soft bounce means that the bounce is only temporary and that if you try again in a day or two, it will most likely not bounce at all. There are multiple things you can do to reduce the risk of soft bounces. The top 4 checks we recommend at Zaplify are:
Make sure that you don't reach out from a brand new domain. If you are using a brand new domain, make sure to warm it up slowly before going full throttle with Zaplify.
If your email address that you are using with Zaplify usually doesn't send a lot of emails, there is a risk that your email activity will seem suspicious at first if you go too hard with Zaplify the first couple of weeks when starting an email campaign. Make sure to set your campaign schedule to a level that is best fit for your account.
Your emails might be marked as spam by the recipient. Usually, this happens if they contain irrelevant or too generic content, or simply if the emails are targeting an audience irrelevant to your content (read more)
Make sure that your email domain is set up using best practices such as SPF-, DKIM- and DMARC DNS records in place. If you don't know what these are, you can ask your email administrator or IT admin.
How to know if an email is a soft bounce?
Some emails that are returned as undeliverable may not tell you why they couldn't be delivered, but most will provide a message or a code that indicates the bounce type. Knowing and interpreting bounce codes is the first step to distinguishing between these two types of undeliverable emails.
First off, check what the returning email bounce notification says – does it state that your email was "blocked"? If your email was blocked, it typically means that you have been temporarily blocked by the recipient's spam filter. This is one of the most common reasons we see. If the returning email however doesn't state that your email was "blocked", the natural next step would be to check if the email contains a 3-digit reason code, as to why the bounce occurred. Here are the most common soft bounce codes.
Bounce code | Bounce type | Description |
421 | Soft | Service not available |
450 | Soft | Mailbox unavailable |
451 | Soft | Error in processing |
452 | Soft | Insufficient system storage |
520 | Soft | Other or undefined mailbox status |
521 | Soft | Mailbox disabled, not accepting messages |
522 | Soft | Mailbox full |
531 | Soft | Mail system full |
545 | Soft | Network congestion |
553 | Soft | Too many recipients |
If you feel like you are experiencing a high bounce rate (above 10%), we would recommend writing in the support chat and we will investigate further.
All bounce codes
For the techy reader, it might be useful to know more about all types of bounces, even the hard ones. Just in case, we have gathered a more comprehensive list below.
Bounce code | Bounce type | Description |
421 | Soft | Service not available |
450 | Soft | Mailbox unavailable |
451 | Soft | Error in processing |
452 | Soft | Insufficient system storage |
500 | Hard | Address does not exist |
510 | Hard | Other address status |
511 | Hard | Bad destination mailbox address |
512 | Hard | Bad destination system address |
513 | Hard | Bad destination mailbox address syntax |
514 | Hard | Destination mailbox address ambiguous |
515 | Hard | Destination mailbox address valid |
516 | Hard | Mailbox has moved |
517 | Hard | Bad sender’s mailbox address syntax |
518 | Hard | Bad sender’s system address |
520 | Soft | Other or undefined mailbox status |
521 | Soft | Mailbox disabled, not accepting messages |
522 | Soft | Mailbox full |
523 | Hard | Message length exceeds administrative limit |
524 | Hard | Mailing list expansion problem |
530 | Hard | Other or undefined mail system status |
531 | Soft | Mail system full |
532 | Hard | System not accepting network messages |
533 | Hard | System not capable of selected features |
534 | Hard | Message too big for system |
540 | Hard | Other or undefined network or routing status |
541 | Hard | No answer from host |
542 | Hard | Bad connection |
543 | Hard | Routing server failure |
544 | Hard | Unable to route |
545 | Soft | Network congestion |
546 | Hard | Routing loop detected |
547 | Hard | Delivery time expired |
550 | Hard | Other or undefined protocol status |
551 | Hard | Invalid command |
552 | Hard | Syntax error |
553 | Soft | Too many recipients |
554 | Hard | Invalid command arguments |
555 | Hard | Wrong protocol version |
560 | Hard | Other or undefined media error |
561 | Hard | Media not supported |
562 | Hard | Conversion required and prohibited |
563 | Hard | Conversion required but not supported |
564 | Hard | Conversion with loss performed |
565 | Hard | Conversion failed |
570 | Hard | Other or undefined security status |
571 | Hard | Delivery not authorized, message refused |
572 | Hard | Mailing list expansion prohibited |
573 | Hard | Security conversion required but not possible |
574 | Hard | Security features not supported |
575 | Hard | Cryptographic failure |
576 | Hard | Cryptographic algorithm not supported |
577 | Hard | Message integrity failure |
911 | Hard | Hard bounce with no bounce code found It could be an invalid email or rejected email from your mail server (such as from a sending limit) |