SMTP error code 553 typically occurs when the recipient's mail server rejects the email message. However, the specific reason for rejection may vary depending on the environment.
Some of the most common reasons for rejection are:
To resolve this issue, ensure that the IP address and domains are within a blocklist. Additionally, ensure that the email does not have signs associated with spam or malware that may cause a false-positive trigger from the security controls, such as a spam filter.
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