NETWORK?

XMail assumes, that you have a network problem or a bad routing to
the recipient's host. This error comes up, when a connection is 
dropped or cannot be established.

Possible reasons for this are
- The recipient's address is malformed
- The recipient's SMTP server dropped the connection, because his
  RDNS check has failed.
- The recipient's SMTP has connection problems.
- The recipient cannot be found due to a DNS config issue.
- Your TCP/IP packets are lost on the route to the recipients SMTP
  (MX Server).
  
Things to check:

Your Firewall
 If you are behind a F-Secure (or similar) firewall and this error 
 only happens when sending large attachments, then your problem IS 
 the firewall. In that case you should contact the FW support or 
 migrate to another firewall.

Your routing
 To verify a recipient's host side problem, get the destination's 
 MX record from the SLOG file. Then do a

 tracert mx_record_of_recipient  (on WINDOWS)
 traceroute mx_record_of_recipient  (on UNIX like platforms)

 This will print the routing and the time until your packets arrive
 on each node on your route. It will also tell you the exact node,
 where the routing is interrupted (marked with a '*' and no time value).

 When you can verify a bad routing and your packets are not lost
 inside your LAN, then you have no further influence on this
 NETWORK issue. Just leave the mail inside the queue and defrost it
 from time to time until it gets through (or increase the timeout 
 until XMail freezes messages).

Your DNS config
 Do a 
 telnet recipient's_SMTP_name 25
 from your XMail machine. If its name cannot be resolved, then it
 might be a DNS problem. If you run your own DNS, check its config.
 Check the contents of MailRoot/dnsroots. If suitable, you can 
 overwrite the contents of this file with one or more DNS server 
 IPs, from which you know they are working 100%. Restart XMail 
 after changes.

Your RDNS entry
 To check your RDNS entry, use the services under
 http://www.dnsstuff.com
 Does your mail_from match your RDNS entry?
 If your mail was generated by a PHP script, make sure that 
 SMTP_FROM is set to a valid host name in your PHP.INI.

Your hardware
 If you can exclude the above then please check if
 - Your network hardware (NIC, cabling, switch, HUB etc.) 
   is intact and
 - your router and firewall are setup correctly.
