Re: [exim] Smtp not possible from some clients

On 2014-12-04 20:44, matthiasmueller07@??? wrote:
> Hello,
Hi,

> I have a problem with the smtp connection from some clients web
> application which is using a smtp connection to send mails. The output
> only says that no smtp conenction is possible, therfore I do not have
> a detailed error message.
Can you activate some sort of debug logging in this web application?

> On the server side I searched the firewall entries, the receiving of
> the TCP packages and the logs. I only found the following log entrie,
> when the Client is connecing to the smtp server which seems to be
> failed.
Did you analyse the TCP dump in Wireshark? Can you see a valid SMTP
handshake between the web app and your Exim server?
Can you manually initiate an SMTP session from the web application's
host?

Is the web application using an encrypted or unencrypted connection?
If it's encrypted a common error might be that the web application fails
to
validate your mail servers certificate and aborts the connection.

> Message:
> no host name found for IP address xx.xx.xx.xx
That's just informational and would not cause Exim to abort a
connection.

> I searched very long time but do not found a real solution I can do on
> my side. I tried to whitelist the ip address or Change the host_lookup
> option but the issue still occur. Also I checked installed fail2ban
> logs but there is also no helpful entry. The Connection from outher
> Clients is working so it seems to be not a general issue.
IIRC, fail2ban is for blocking brute force SSH login attempts, it won't
interfere
with SMTP.

How flexible is your environment? If you can't enable debugging in the
web application
and Wireshark is no help either, you could always run Exim in debugging
mode on a
different port or server and see what Exim has to say about this
connectivity issues.

Hth,
Tom.