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I have a email system using zimbra opensource.

My system have 2 MTA server and relay outbound to a Barracuda Spam Gateway.

The follow send outbound email: Client --(1)--> MTA --(2)--> Barracuda --(3)--> Internet --(4)--> Reception server

When users in my system get infected with the virus and send a lot of spam to the outside then in MTA zimbra log, I got this error at connection (2) between MTA and Barracuda: (For almost email sending in this time)

Dec 12 00:18:00 mta1 postfix/smtp[21868]: 1683011C254D: to=, relay=x.x.x.x[x.x.x.x]:25, delay=0.07, delays=0.03/0.02/0.01/0, dsn=4.4.2, status=deferred (lost connection with x.x.x.x[x.x.x.x] while sending RCPT TO)

(x.x.x.x is Barracuda IP)

On the barracuda server I did not see any connection information at the time.

I think this is some parameter of zimbra or postfix limiting the sending of too many emails to one address in a time period.

Does anyone know about this bug? Please help me. Thank you very much!

  • I'm not sure if Zimbra includes rate limiting by default but it wouldn't surprise me, but I'm not sure where it would be set in the dashboard. The postfix configuration is around destination_recipient_limit and destination_concurrency_limit. However, Barracuda can also rate limit and your log line suggests that it is, and it's more likely to be a firewall component rather than postfix, either a laver 3 firewall like iptables or a layer 7 firewall such as nginx. – Simon Greenwood Dec 13 '17 at 7:52

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