SMTP error 522 typically occurs when the client IP address is within a blocklist on the recipient's email server or the email server's security controls.
IP addresses usually get blocklisted due to malicious or suspicious activity, and one of the easiest ways of getting blocklisted is by sending bulk emails or marketing campaigns.
It is vital to verify with the recipient's email server to ensure that the client's IP address is not within any of the blocklists or that any security controls do not block the client's IP address.
If the client's IP address is within a global or public blocklist, the client may proceed with the appeal process to remove the specific IP address from the blocklist.
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