Hello :)

I've been searching for ages on this and not been able to find a solution.

I have one Exchange 2013 server running all roles except Edge Transport on a domain member server, and one running Edge Transport in a workgroup. There is a VPN connecting the two servers and temporarily for troubleshooting the firewall is configured to allow everything to pass between them.

When I send an email (from Exchange to an external domain) it successfully makes it into the Edge Transport server queue but then I get the error:

DNS server returned ErrorRetry reported by 255.255.255.255. 

(Sometimes the IP in the error is 0.0.0.0)

I have configured the Hub Transport server's external DNS settings, and ticked the box on both send connectors to use external DNS. I have run Start-EdgeSynchronization (which was successful) but I still get the same errors.

The error occurs for all domains, the thing I don't get is why it's reporting the DNS server as being either 0.0.0.0 or 255.255.255.255 in the error message - which would point to it not knowing which servers to actually use. I've also tried manually telling it via `Set-TransportServer -ExternalDNSServers 8.8.8.8` but that doesn't work either.

Get-SendConnector | FL (run on the edge server) returns:

AddressSpaces                : {smtp:*;100}
AuthenticationCredential     :
CloudServicesMailEnabled     : False
Comment                      :
ConnectedDomains             : {}
ConnectionInactivityTimeOut  : 00:10:00
DNSRoutingEnabled            : True
DomainSecureEnabled          : True
Enabled                      : True
ErrorPolicies                : Default
ForceHELO                    : False
Fqdn                         :
FrontendProxyEnabled         : False
HomeMTA                      :
HomeMtaServerId              :
Identity                     : EdgeSync - Default-First-Site-Name to Internet
IgnoreSTARTTLS               : False
IsScopedConnector            : False
IsSmtpConnector              : True
MaxMessageSize               : 10 MB (10,485,760 bytes)
Name                         : EdgeSync - Default-First-Site-Name to Internet
Port                         : 25
ProtocolLoggingLevel         : None
RequireOorg                  : False
RequireTLS                   : False
SmartHostAuthMechanism       : None
SmartHosts                   : {}
SmartHostsString             :
SmtpMaxMessagesPerConnection : 20
SourceIPAddress              : 0.0.0.0
SourceRoutingGroup           : Exchange Routing Group (DWBGZMFD01QNBJR)
SourceTransportServers       : {}
TlsAuthLevel                 :
TlsCertificateName           :
TlsDomain                    :
UseExternalDNSServersEnabled : True

AddressSpaces                : {smtp:--;100}
AuthenticationCredential     :
CloudServicesMailEnabled     : False
Comment                      :
ConnectedDomains             : {}
ConnectionInactivityTimeOut  : 00:10:00
DNSRoutingEnabled            : False
DomainSecureEnabled          : False
Enabled                      : True
ErrorPolicies                : Default
ForceHELO                    : False
Fqdn                         :
FrontendProxyEnabled         : False
HomeMTA                      :
HomeMtaServerId              :
Identity                     : EdgeSync - Inbound to Default-First-Site-Name
IgnoreSTARTTLS               : False
IsScopedConnector            : False
IsSmtpConnector              : True
MaxMessageSize               : Unlimited
Name                         : EdgeSync - Inbound to Default-First-Site-Name
Port                         : 25
ProtocolLoggingLevel         : None
RequireOorg                  : False
RequireTLS                   : False
SmartHostAuthMechanism       : ExchangeServer
SmartHosts                   : {--}
SmartHostsString             : --
SmtpMaxMessagesPerConnection : 20
SourceIPAddress              : 0.0.0.0
SourceRoutingGroup           : Exchange Routing Group (DWBGZMFD01QNBJR)
SourceTransportServers       : {}
TlsAuthLevel                 :
TlsCertificateName           :
TlsDomain                    :
UseExternalDNSServersEnabled : True

Would really appreciate any help! Thanks.

Alex

Nevermind, done a bit more digging and the following run on the edge server started mail flowing:

Set-TransportService -ExternalDNSAdapteEnabled $False -ExternalDNSServers 8.8.8.8

Cheers.

Hi Alex,

How's going on before this issue arise? What have you changed?

For your question, please use ExRCA to test inbound and outbound mail flow.
Since you use Edge Synchronization, the connectors on the Edge server are managed on the mailbox server, please check the setting on mailbox server. Besides, login EAC and switch to Servers, then check the setting for DNS lookups on mailbox server. Use NSLOOKUP to make sure that your Edge server can resolve Internet DNS MX records.

More details about Troubleshooting Mail Queues That Are Increasing on Edge Transport Servers, for your reference:
https://technet.microsoft.com/en-us/library/bb851512(EXCHG.80).aspx