Please clarify - are those lines excerpted from a LISTSERV log, or from the log of an SMTP service - your Subject on the message is somewhat confusing? (I don't even know what a "Lisert" is, actually.) To make a few wild guesses, it looks like maybe one of your services is stopped, or confused, or starved for resources, or perhaps a firewall is interfering with connectivity, or maybe the physical network (nic,hub/switch,cable) is going flaky. If you reboot the system and try again, does this problem recur? At the risk of being very boring, I will repeat advice you have been given here before - You will NOT get useful results with the IIS SMTP service. You need to implement some other mail handler product to handle your LISTSERV activity. Also, a Google search on "[10053]" brought up several items, I picked this one out of the list: http://www.altn.com/support/FAQ_Article.asp/product_id/MDaemon/Number/KBA-01510 >>> [log in to unmask] 4/26/2006 12:04:00 PM >>> Can someone explain mean what is happening here? 6 Apr 2006 08:42:57 Send error: Unknown error [10053] 26 Apr 2006 09:49:56 Receive error: Unknown error [10053] 26 Apr 2006 10:06:53 -> RSET 26 Apr 2006 10:06:53 451 Timeout waiting for client input 26 Apr 2006 10:34:53 Receive error: Unknown error [10053] 26 Apr 2006 11:02:52 Receive error: Unknown error [10053] 26 Apr 2006 11:36:54 -> RSET 26 Apr 2006 11:36:54 451 Timeout waiting for client input I'm using IIS SMTP by the way. thx