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Hi all,
in the last couple of days we've been presenting some delay problems sending and receiving mails, we've been receiving a lot of spam and the queue is growing up to 2000 messages. Today I was checking some settings at the "SMTP Server" configuration and change the option "Maximum number of delivery threads" from 32 to 50. My question is: how do you think is the recomended number of threads?
Our Kerio server is connected to a 3 MB/s dedicated internet connection and is running on a virtual machine (VMware ESX3i) with 8G ram and 2 quad core, running Centos 5.4.

Thank and Best Regards,
id t

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dedicated Intel XServe3,1 (late 2009), 8-core, 12GB of RAM, around 150 users over a 100MB connection, 1024 threads, never over 80% of (one) core.
Pavel Dobry (Kerio)

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Using more than 50 delivery threads is possible only in few exceptional cases (when using no anti-virus or anti-spam). Otherwise there is no big performance benefit. 1024 is extremely high value.

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1024 delivery threads is a very high setting. With a bit of bad luck (or the wrong kind of worm loose on the LAN), you run the risk of opening 1024 simultaneous deliveries to the same server. If the receiver doesn't have any kind of throttling, it will probably crash or exhaust most of its TCP/IP sockets. It is effectively a denial-of-service attack. At the very least, 1024 simultaneous connections will probably congest you WAN link and make the server hard to reach.

In any case, Windows 2003 can by default have 3977 outbound connections open at the same time. That's not a lot left when you consider webmail, KOC/KOFF, IMAP, DNS lookups and whatnot.

Just my 2 cents ...

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