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This issue happens because the recipient’s MTA rejected an email from TMEMS without authentication.

The authentication rule is configured by the recipients themselves, and TMEMS can do nothing for these outbound emails.

Keywords: outbound emails are rejected,emails sent to a specific recipient server are bounced,error 550 when sending emails to a recipient server

"550 authentication required" error is seen when outbound mails are bounced in Trend Micro Email Security (TMEMS)

Trend Micro Email Security All

Last updated: 2025/05/08

Solution ID: KA-0012586

Category: Troubleshoot

Outbound mails which passes through TMEMS are being rejected by the recipient server, and returns an NDR which says "550 authentication required".

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This issue happens because the recipient’s MTA rejected an email from TMEMS without authentication.

The authentication rule is configured by the recipients themselves, and TMEMS can do nothing for these outbound emails.

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