Exchange 2007: 421 4.3.2 Service not available, closing transmission channel

hello,

i have 4 servers that have moved to a new subnet, and therefore got each a new ip address:
1 x Terminal Server (win 2008)
1 x Exchange 2007 (win 2008)
1 x Domain Controller (win 2008)
1 x Domain Controller (win 2008)

all services are started properly and everything seems to works fine: active directory, drive mappings, outlook on the terminal server opens the exchange mailbox properly, and users are able to send e-mails out.

however, receiving e-mails doesn't work.. it turns out that when you telnet port 25 on the exchange server, you get the following message:

421 4.3.2 Service not available, closing transmission channel

in the event viewer, the following error keeps happening; not sure if this is related to the issue:

MsExchange System Attendant Mailbox EventID 4001

A transient failure has occurred. The problem may resolve itself in awhile. The service will retry in 56 seconds. Diagnostic information:

Cannot open mailbox /o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=354-008/cn=Microsoft System Attendant.
Microsoft.Exchange.Data.Storage.ConnectionFailedTransientException: Cannot open mailbox /o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=354-008/cn=Microsoft System Attendant. ---> Microsoft.Mapi.MapiExceptionLogonFailed: MapiExceptionLogonFailed: Unable to open message store. (hr=0x80040111, ec=-2147221231)
Diagnostic context:
    Lid: 18969   EcDoRpcExt2 called [length=254]
    Lid: 27161   EcDoRpcExt2 returned [ec=0x0][length=116][latency=0]
    Lid: 23226   --- ROP Parse Start ---
    Lid: 27962   ROP: ropLogon [254]
    Lid: 17082   ROP Error: 0x80040111
    Lid: 26937  
    Lid: 21921   StoreEc: 0x80040111
    Lid: 27962   ROP: ropExtendedError [250]
    Lid: 1494    ---- Remote Context Beg ----
    Lid: 26426   ROP: ropLogon [254]
    Lid: 59409  
    Lid: 45073  
    Lid: 11173   StoreEc: 0x80040111
    Lid: 22970  
    Lid: 8620    StoreEc: 0x80040111
    Lid: 1750    ---- Remote Context End ----
    Lid: 26849  
    Lid: 21817   ROP Failure: 0x80040111
    Lid: 26297  
    Lid: 16585   StoreEc: 0x80040111
    Lid: 32441  
    Lid: 1706    StoreEc: 0x80040111
    Lid: 24761  
    Lid: 20665   StoreEc: 0x80040111
    Lid: 25785  
    Lid: 29881   StoreEc: 0x80040111
   at Microsoft.Mapi.MapiExceptionHelper.ThrowIfError(String message, Int32 hresult, Int32 ec, DiagnosticContext diagCtx)
   at Microsoft.Mapi.ExRpcConnection.OpenMsgStore(OpenStoreFlag storeFlags, String mailboxDn, Guid mailboxGuid, Guid mdbGuid, MapiStore msgStorePrivate, String& correctServerDn, ClientIdentityInfo clientIdentityAs, String userDnAs, String applicationId, CultureInfo cultureInfo)
   at Microsoft.Mapi.ConnectionCache.OpenMapiStore(String mailboxDn, Guid mailboxGuid, Guid mdbGuid, ClientIdentityInfo clientIdentity, String userDnAs, OpenStoreFlag openStoreFlags, CultureInfo cultureInfo, String applicationId)
   at Microsoft.Mapi.ConnectionCache.OpenMailbox(String mailboxDn, Guid mailboxGuid, Guid mdbGuid, WindowsIdentity windowsIdentityAs, String userDnAs, OpenStoreFlag openStoreFlags, CultureInfo cultureInfo, String applicationId)
   at Microsoft.Exchange.Data.Storage.ConnectionCachePool.OpenMailbox(String serverDn, String userDn, String mailboxDn, Guid mailboxGuid, Guid mdbGuid, Object identity, ConnectFlag connectFlag, OpenStoreFlag openStoreFlag, CultureInfo cultureInfo, String clientInfoString, Boolean secondTry)
   --- End of inner exception stack trace ---
   at Microsoft.Exchange.Data.Storage.ConnectionCachePool.OpenMailbox(String serverDn, String userDn, String mailboxDn, Guid mailboxGuid, Guid mdbGuid, Object identity, ConnectFlag connectFlag, OpenStoreFlag openStoreFlag, CultureInfo cultureInfo, String clientInfoString, Boolean secondTry)
   at Microsoft.Exchange.Data.Storage.ConnectionCachePool.OpenMailbox(String serverDn, String userDn, String mailboxDn, Guid mailboxGuid, Guid mdbGuid, Object identity, ConnectFlag connectFlag, OpenStoreFlag openStoreFlag, CultureInfo cultureInfo, String clientInfoString, Boolean secondTry)
   at Microsoft.Exchange.Data.Storage.ConnectionCachePool.OpenMailbox(String serverDn, String userDn, String mailboxDn, Guid mailboxGuid, Guid mdbGuid, Object identity, ConnectFlag connectFlag, OpenStoreFlag openStoreFlag, CultureInfo cultureInfo, String clientInfoString)
   at Microsoft.Exchange.Data.Storage.MailboxSession.Initialize(LogonType logonType, ExchangePrincipal owner, DelegateLogonUser delegateUser, Object identity, OpenMailboxSessionFlags flags)
   at Microsoft.Exchange.Data.Storage.MailboxSession.CreateMailboxSession(LogonType logonType, ExchangePrincipal owner, DelegateLogonUser delegateUser, Object identity, OpenMailboxSessionFlags flags, CultureInfo cultureInfo, String clientInfoString)
   at Microsoft.Exchange.Data.Storage.MailboxSession.OpenAsAdmin(ExchangePrincipal mailboxOwner, CultureInfo cultureInfo, String clientInfoString, Boolean useLocalRpc, Boolean ignoreHomeMdb)
   at Microsoft.Exchange.Data.Storage.MailboxSession.OpenAsAdmin(ExchangePrincipal mailboxOwner, CultureInfo cultureInfo, String clientInfoString)
   at Microsoft.Exchange.Servicelets.SystemAttendantMailbox.Servicelet.Work()


i have researched this error message and found a lot of microsoft articles and other sites, but nothing was really applying to this case...

can anyone guide me through the proper troubleshooting process for this ?

thanks a lot!