Common causes
- The recipient’s mailbox is full.
- The receiving server is down or overloaded.
- The email is too large.
- The receiving provider is temporarily limiting how many messages it accepts from your server.
What to do about soft bounces
Most email platforms retry soft bounces automatically for a few days. If the same address soft-bounces several campaigns in a row, treat it like a hard bounce and remove or suppress it, because repeated failures also hurt your sender reputation.