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sendmail and Exchange 2010

Valued Contributor

sendmail and Exchange 2010

Hello Everyone,


We are currently moving from Exchange 2003 to Exchange 2010.


For some reason we are getting "Deffered: connection refused" when sending an email through smart relay. Yes the is setup correctly because the only thing I changed was the DS entry.


Now two interesting things... The server that is giving me the connection refused messate is HP-UX 11.31. if i do the same thing from a HP-UX 11.11 server it gives me a "Deffered: connection timed out". Next, even though it appears that nothing is being relayed eventually it all comes out at once. The server that is giving a "Deffered: connection refused" takes over an hour but the server giving the "Deffered: connection timed out" usually goes out in 5 - 10 minutes.


Has anyone run into this and what did you do to correct it?


Any help would be greatly appreciated!






P.S. This thread has been moevd from HP-UX > System Administration to Messaging. - Hp forum moderator

Honored Contributor

Re: sendmail and Exchange 2010

A "Deferred: connection timed out" might indicate that there is a firewall somewhere between the HP-UX server and the Exchange smart relay, dropping the connection. A 5-10 minute timeout fits this picture, since sendmail makes multiple TCP connection attempts before giving up. This is clearly a connectivity issue, so Sendmail reports this immediately.


A "Deferred: connection refused" means that the TCP connection was apparently rejected by the smart relay. The reason it takes over an hour to be reported might be because of Sendmail's own internal logic.


If a mail server is too busy, it can stop listening for incoming connections so that it can complete processing of mails that are already in the server. Sendmail expects this and just re-queues the mail for a later re-send attempt.  With the default settings, if a mail is still unsent after an hour, the sender will get a notification mail from Sendmail that the delivery might take a while. Sendmail still keeps the mail in the outgoing queue and will make periodic attempts to send it (that's what "deferred" means). The period of delivery attempts is controlled with the -q option to the sendmail daemon: typical configurations are to re-attempt delivery hourly or every 30 minutes.


Typically, if the mail is still in the outgoing queue after 5-7 days have passed, Sendmail will create a final delivery failure notification for the original sender and give up.


In Exchange Server 2007, several anti-spam and encryption features were added to Exchange. In Exchange 2010, I guess some of them might be enabled by default: for example, the plain old unauthenticated SMTP in port 25 may not necessarily be allowed by default.