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Zimbra SMTP Amavis Integration
Port 10025 is commonly used internally within Zimbra Collaboration Suite to facilitate the relay of email messages from the Amavis content filter back into the Postfix Mail Transfer Agent (MTA). This port enables scanning and filtering of emails for malware, spam, or policy compliance before final delivery, serving as a secure and structured point of reinjection after content analysis..
Port 10025 is primarily utilized in mail server infrastructures, especially those leveraging the Zimbra Collaboration Suite, which integrates Postfix as its core MTA along with Amavis for antivirus and antispam filtering. When an email enters Zimbra’s Postfix instance, it can be routed through Amavis for content filtering. After filtering and analysis, the email is then passed back into Postfix on port 10025 for further processing toward the intended recipient mailbox.
This reinjection architecture helps to separate clean email traffic from unverified or potentially malicious content. Amavis listens on one port (commonly 10024) to receive emails from Postfix, performs its filtering, then relays the sanitized message to Postfix on port 10025. This workflow ensures scanned emails can be tracked and managed distinctly, simplifying filtering logic and contributing to a layered security posture.
Normally, port 10025 is bound to localhost or internal network interfaces, as it’s intended purely for inter-process communication within the mail system. It’s not an Internet-facing or client-used port like 25 or 587, meaning it serves a specialized, backend role in the mail delivery pipeline within Zimbra hosts.