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: 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!