You confused me with the error codes you've provided !
but...... check this pdf - it shows the error codes !
http://www.answersthatwork
421 <Server name>Service not available the sending email program should try again later (also called SMTP Error 4.2.1)
SMTP Error 421 : The Mail transfer service is unavailable because of a transient event. SMTP reply 451 can be
caused by many things but generally indicates that the mail server which returns this status code is currently
unavailable but may be available later.
For example, the server administrator may have stopped the mail service to troubleshoot a problem, or the mail
server is right in the middle of rebooting, or the mail server is currently processing too many incoming messages or
incoming requests, etc.... Note : Mail Server in this case can be any of the mail servers on the messages
route the sending server (your server), the ISP SMTP server, or the recipients mail server.
Clearly, if you repeatedly receive an SMTP status 421 then the problem is no longer of a transient nature and you
need to investigate or inform the relevant network administrator, ISP tech support, or the recipient.
441 The recipients server is not responding (also called SMTP Error 4.4.1)
SMTP Error 441 : This is an error emanating from your server indicating that the recipients server is not
responding. Your server will automatically try again a number of times how many depends on how your server
has been configured.
Check your SMTP communication:
http://support.microsoft.c
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by: MCSA2003Posted on 2009-08-04 at 18:28:16ID: 25019625
Try running this command in exchange management shell
netsh interface tcp set global autotuning=disabled