Problem Could not connect to SMTP host, mailing problem

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Hello everyone,

I have a strange problem when sending mail to specific domain / domains, so I'm hoping that you expert's can help me.

E mail's bounce back with this error:

This is why I was unable to deliver your message:
Could not connect to SMTP host: my.mx.dns, port: 25, response: -1

We have third party e-mail server, called DeskNow, in DMZ and ISA server 2006. When we send e-mail to domain from our ISP, where we have mx records for our mail server, and to our client's that use the same ISP, e-mails bounce back with above mentioned error !?

I have contacted our ISP to check that maybe is our server blacklisted, they say that it isn't.

Telnet from my mail server works, i can connect to port 25.

Do you have any idea what is going on ? Please help me because this is driving me nuts!

Thnx.

 

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you can check your domains status on mxtoolbox.com

if it is on a blacklikst, your recipients mailserver may well drop your mail.

if you can expand a bit on your set-up (including logs) we can try to help.

any reason you are using a host opposed to sending via smtp?

if it is one, or two domains out of several, could it be a problem their end?

 

I have checked blacklist status on my domain and here is the result:

Backscatter.org LISTED Sorry 195.29.118.163 is blacklisted at Detail
Return codes were: 127.0.0.2 765 343

UCEPROTECTL3 LISTED Your ISP T-HT T-Com Internet network/AS5391 is UCEPROTECT-Level3 listed for hosting a total of 2518 abusers. See: Detail
Return codes were: 127.0.0.2 765 328


I dont understand this UCEPROTECTL3 thing.

UCEPROTECTL1 says that my IP address is not listed.
UCEPROTECTL2 says that my network IP is not listed.

UCEPROTECTL3 on the other hand says that my provider is on blacklist ? Is that the reason that mail's are bouncing ?


Sorry but i dont unterstand host opposed thing.. I'm sending mail through SMTP so i dont get it ?

I will put logs and configuration in few minutes..

 

your mailserver is blacklisted.

backscatter.org will give you a time +/- ten minutes. take a look and see what happened around this time.

mail is either sent directly (using dns) or a smart host; your isp.

you can check where the mail originates from the mail header - send one to your own personal account.

one thing with the backscatter register: make sure you are confident you have fixed the problem before asking to be removed otherwise it can become harder should the problem re-arrise.

 

It's possible that because you are both using the same ISP then both of your hosted mail servers are also the same and are interfering with each other.

Can the other company send you mail and you receive it okay?

I had a similar problem with another company. We had the mail server hosted with an ISP at the time and we formed another company. They used the same ISP for their hosted mail and the 2 companies were hosted on the same mail server on their end. The end result was that we could send them mail but they couldn't send us mail.

 

I have contacted that other company and they say that also have mail issues. Maybe it's problem with ISP.

About blacklist, i dont have log's from that specific date blackscatter.org is providing. My mail server is configured to preserve logs for 5 days only.