A bounce is an email that could not be delivered and comes back to you with an error message. Instead of reaching the recipient's inbox, it is refused by the receiving server. In prospecting, a few bounces are normal, but a high rate is a warning sign: it damages your sending reputation and jeopardizes the rest of your campaigns.
Hard bounce and soft bounce
Not all bounces are equal, and the distinction guides how you react.
A hard bounce is a permanent failure. The address does not exist, the domain is wrong, or the account has been closed. There is no point retrying: the message will never arrive. These addresses must leave your list immediately, because keeping them only worsens the problem with every send.
A soft bounce is a temporary failure. The recipient's mailbox is full, the message is too heavy, or the receiving server is briefly unavailable. The address is valid, but delivery failed at that moment. A later retry often succeeds. If soft bounces keep repeating for the same address, treat it like a hard bounce and remove it.
Why bounces threaten your deliverability
Inboxes watch your sending behavior. A high bounce rate suggests to them that you are writing to a list you do not keep up to date, a classic spam signal. In response, they filter your messages more harshly, including those meant for perfectly valid addresses. A single bad send can therefore penalize an entire campaign.
Keeping the rate low is basic hygiene, then. Remove hard bounces without delay, verify your addresses before sending, and be wary of bought lists, often filled with dead addresses that trigger bounces in bulk. Sending to a shorter but clean list protects your ability to reach the inbox over the long run.
How Kaptor helps you keep a low bounce rate
Kaptor draws on real sources to gather contacts by trade and area, which limits fanciful addresses from the start. You send from your own inbox and track the status of every message, so an address that fails is spotted right away instead of lingering in your list.
To grasp the full set of factors that decide whether an email arrives, read our page on deliverability. And to lay a sound technical foundation, see how email authentication works.