SBS2011 Exchange 2010 mail stuck in smtp queue with " 451 4.4.0 primary target ip address responded with 421 4.2.1 unable to connect" error

Posted on 2012-08-30
Last Modified: 2012-08-30
Hi everybody,

After having done a migration from a SBS2003 server to a new SBS2011 server, i'm getting a strange pb, all mail sending from my users are stuck in smtp queue on exchange 2010 whith 451 4.4.0 primary target ip address responded with: 451 4.4.0 primary target ip address responded with 421 4.2.1 unable to connect error".

SBS2011 use a smtp relay with no authentification to relay mail (Internet Provider SMTP relay), the following commands are OK  from my server to the smtp relay :

telnet smtp.xxxx.yy 25
mail from:
rcpt to:
subject: test

Doing this the mail is sending without pb

I've also test DNS with nslookup with good results.
I've recreate the sending connector on my exchange 2010 ECM with smtp,*,1 and network configure to be with no authentification.

Networks and Internet SBS assistant have been done correctly.

Question by:rfedicia
    LVL 52

    Accepted Solution

    Is there a Send Connector is it pointing to some Smarthost ?
    Does the Send connector has the new 2010 server as Bridgehead server ?

    - Rancy
    LVL 52

    Expert Comment

    by:Manpreet SIngh Khatra
    Is your Router configuration and settings changed for the new server ?
    If you have a router or firewall .... you need to enable it to receive emails from the HUB server and route external and same way to receive emails from external and be able to send to HUB for delivery.

    - Rancy

    Author Comment

    I've just solved the problem, the Windows SBS Internet Send connector was not created correctly, after recreate it from sbs wizard and disativate the exchange send connector that i've created, the queue are empty, all the mail are gone.

    Thanks Rancy
    LVL 52

    Expert Comment

    by:Manpreet SIngh Khatra
    Dont mind but B anything better i could do for A :)
    Just want to try and give my best shot at things :)

    - Rancy

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