When sending email from Archive Manager web interface you recieve an error: "An established conne (4211138)

When sending email from Archive Manager web interface you recieve an error:
"An established connection was aborted by the software in your host machine"

There is also an event logged in the Windows Application event log on the Archive Manager server stating the following:

Event Type:  Error
Event Source:  Archive Manager
Event Category:  None
Event ID:  0
Date:    2/28/2008
Time:    2:09:14 PM
User:    N/A
Computer:  BKF-QUEST
Description:
Exception has been caught in the application

Exception Source:           System
Exception Type:               System.Net.Sockets.SocketException
Exception Message:         An established connection was aborted by the software in your host machine
Exception Target Site: Connect
Date and Time:                 2/28/2008 10:09:14 AM
Machine Name:                   BKF-QUEST
IP Address:                       10.1.1.14
Current User:                   DOMAIN_BKF\ArchiveMgr_Service
CLR Version:                     1.1.4322.2407
Platform (version):       Win32NT (5.2.3790.0)
Application Domain:       /LM/W3SVC/2/Root-1-128487222973091994
Assembly Codebase:         file:///C:/Program Files/ArchiveManager/ArchiveManagerWebsite/bin/AfterMail.WWW.DLL
Assembly Fullname:         AfterMail.WWW, Version=3.7.0.459, Culture=neutral, PublicKeyToken=null
Assembly Version:           3.7.0.459
Exception Source:           System
Exception Type:               System.Net.Sockets.SocketException
Exception Message:         An established connection was aborted by the software in your host machine
Exception Target Site: Connect

---- Stack Trace ----
    at System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
    at AfterMail.Utility.Mime.SMTPCommunicator.xca4f40515dc04b2b()
    at AfterMail.Utility.Mime.S