PMG 8 x Exchange 2019 trouble


New Member
Jun 13, 2023
Hi everyone :) !

I'm using pmg version 8 and Exchange 2019 u12 version.

This is my infrastructure information.

MX -> ->
A -> ->
A -> ->

My machine is under hyper-v, all with public ip.
my forest is

I can receive mail to exchange mailbox by pmg. but i can't send :/ !
My Send-Connecter is set to port 26 and i route with smart host by the ip of pmg.
when i try to send mai,i have this following error in my Message Tracking log.

DiagnosticInfo=Error: RetrySmtp, Diagnostic Information: Stage:UpdateMsgIdToPoisonContextMapping, SmtpResponse:451 4.4.397 Error communicating with target host. -> 421 4.2.1 Unable to connect -> SocketConnectionRefused: Socket error code 10061, details:FailedRecipientCount:0; RetryRecipientCount:0';S:DeliveryPriority=Low;S:PrioritizationReason=SenderExceededSubmissionRateLimit

And in pmg mail proxy configuration i have add network trusted domain relay etc..

So can you tell me if it's pmg trouble or exchange ?

Thanks you,
SmtpResponse:451 4.4.397 Error communicating with target host. -> 421 4.2.1 Unable to connect -> SocketConnectionRefused:
Not too familiar with Exchange error-messages - but this sounds like you get a connection refused when trying to connect to port 26:
* you can verify this by checking the pmg journal - if nothing is logged there then I assume you either have a different port configured in PMG, or some firewall in between is not allowing the connection.

I hope this helps!
Hi @Stoiko Ivanov, thanks you for your fast response !

There is no firewall enable or beetween the both VMs and in my /var/log/syslog or /var/log/mail.log there is nothing when i try to send a mail by my exchange :/

Also i can telnet my pmg port 25 and 26 by my exchange server the connection is not refused.

I have forget to tell you about my mail stuck in draft after send
Last edited:
If a tcp-connection to port 26 works from the exchange to your PMG (which you tested with telnet) - then I can only assume that something is not configured correctly in the SendConnector

Do you see any traffic coming from your exchange in tcpdump on your PMG?

else - maybe there is some kind of limit in the Exchange - and the refusal happens when you try to send the mail to exchange (and not when exchange tries sending to PMG) - guessing this based on:
when i use telnet i see in tcpdump, but no when i send mail.

So this is my Send-Connector config

AddressSpaces                : {SMTP:*;1}
AuthenticationCredential     :
CloudServicesMailEnabled     : False
Comment                      :
ConnectedDomains             : {}
ConnectionInactivityTimeOut  : 00:10:00
ConnectorType                : Default
DNSRoutingEnabled            : False
DomainSecureEnabled          : False
Enabled                      : True
ErrorPolicies                : Default
ForceHELO                    : False
Fqdn                         :
FrontendProxyEnabled         : False
HomeMTA                      : Microsoft MTA
HomeMtaServerId              : EXCHANGE-2019
Identity                     : Proxmox Mail Gateway
IgnoreSTARTTLS               : False
IsScopedConnector            : False
IsSmtpConnector              : True
MaxMessageSize               : 35 MB (36,700,160 bytes)
Name                         : Proxmox Mail Gateway
Port                         : 26
ProtocolLoggingLevel         : Verbose
Region                       : NotSpecified
RequireOorg                  : False
RequireTLS                   : False
SmartHostAuthMechanism       : None
SmartHosts                   : {[]}
SmartHostsString             : []
SmtpMaxMessagesPerConnection : 20
SourceIPAddress              :
SourceRoutingGroup           : Exchange Routing Group (DWBGOTVJQNBJR)
SourceTransportServers       : {EXCHANGE-2019}
TlsAuthLevel                 :
TlsCertificateName           :
TlsDomain                    :
UseExternalDNSServersEnabled : False

And i don't understand what i need to do with that
it is only parameter for receive connector ?
when i use telnet i see in tcpdump, but no when i send mail.
Then I guess Exchange does not even try to connect to your PMG - so the issue is most likely in your Exchange configuration.

As I really don't have much experience with Exchange I cannot help you with this - maybe you should contact Microsoft Support for resolving issues with Exchange.

it is only parameter for receive connector ?
this was my guess above - that the mail was not accepted by exchange in the first place (because the sender is above the ratelimit) - and thus cannot be forwarded to PMG...


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