A soft bounce occurs when an email cannot be delivered temporarily but may be delivered successfully on a later attempt.
Possible causes of a soft bounce include:
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Recipient's mailbox is full: If the recipient has no free storage space left, the email cannot be delivered.
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Recipient's server is overloaded: The recipient's email server may be temporarily overloaded and therefore unable to receive the email.
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Technical problems on the recipient's server: A temporary problem with the recipient's email server can prevent the email from being delivered.
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Temporary block: The recipient's server temporarily blocks emails, e.g. due to suspected spam or security measures.
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Missing email authentication: Problems with email authentication (e.g. missing SPF, DKIM or DMARC records) can lead to a temporary block.
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Network problems: Connection problems between the sending and receiving servers, such as a poor internet connection, can also cause a soft bounce.
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Missing or incorrect DNS records: If the sender's DNS records are not correct, this can cause problems with email delivery.
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Recipient's email filters: The recipient's server may temporarily block emails because of certain content or characteristics identified as spam.
Tip: Soft bounces are usually temporary, and many email servers try to deliver the message again later. If the soft bounce occurs repeatedly, the cause should be investigated more closely.