Exchange Server dont connect to SMPTP Server

[Elephantino]

Hello everybody!
I need help with this scenario:

On my Centos 7/WHM Server I have Mailboxes with an add-on Domain of customer account.

An Outlook do connect and work with Port 465 ssl/TLS using SSL and 587 STARTTLS.

But my customers Exchange Server Smart Host and connector reach the server but get the fllowing errors and fails:

LED=451 4.4.395 Target host responded with error -> 421 4.4.1 Connection timed out MSG=FQDN=mail.xxxxx.de; IP=162.55.xxx.94;LRT=22.05.2023 11:58:22 587

LED=451 4.4.395 Target host responded with error -> 451 5.7.3 Require basic authentification MSG=FQDN=mail.xxxxxxx.de; IP=162.55.xxx.94;LRT=22.05.2023 12:23:22
Using Port 587

LED=451 4.4.395 Target host responded with error -> 421 4.4.2 Conncetion dropped due to SocketError MSG=FQDN=mail.xxxxxx.de; IP=162.55.xxx.94;LRT=22.05.2023 12:23:22
Using Port 465

Can anybody help and give me a lead to resolve it?

Greetings
Elephantino

 

[cPRex]

Hey there! I'm not completely sure what is happening with this configuration. In general, a smarthost is used by the server to bypass email restrictions imposed by the hosting provider so that server can still send email. This would mean that the server is connecting to the remote smarthost, and not the other way around.

Can you provide me with more information on your specific configuration and use case?

 

[Elephantino]

Hey there! I'm not completely sure what is happening with this configuration. In general, a smarthost is used by the server to bypass email restrictions imposed by the hosting provider so that server can still send email. This would mean that the server is connecting to the remote smarthost, and not the other way around.

Can you provide me with more information on your specific configuration and use case?

Thank you for giving attention to my issue.
Scenario:
1. One of my customers is running a local exchange server 2019.
2. This customer has several email accounts on our CPanel Server.
3. We use an addon domain with his account on our server.
4. He wants to route his outbound emails to our SMTP server named mail.xxxx.de.
5. If he wants to connect to our SMTP server, he is getting the above mentioned errors.
6. We tested the credentials we have given to the customer for login to our SMTP mailserver with an outlook client. Outlook client does connect without any errors.

What I should know:
1. What could be the reason to issue this error messages?
2. Does an exchange server need relay? In this time no relay, just simple SMTP server.
3. Is there a log file showing up such connection errors (location?)?
4. Do we or the customer need special settings to work?

We are thankful for any help.
Greetings,
Elephantino

 

[mtindor]

LED=451 4.4.395 Target host responded with error -> 451 5.7.3 Require basic authentification MSG=FQDN=mail.xxxxxxx.de; IP=162.55.xxx.94;LRT=22.05.2023 12:23:22
Using Port 587

It looks like one of the two is occurring:

1. The exchange server is not sending SMTP Authentication credentials to your server to authenticate
OR
2. The exchange server is using the wrong authentication protocol when trying to authenticate (NTLM, Kerbosos, CRAM-MD5, Plain, etc)

You should be able to get more details by grep'ing the IP address of the Exchange server WAN connection against your /var/log/exim_mainlog

m