Can't Send Email

I have a client who can no longer send emails. The set up they have consists of a server running Windows Server 2003 SBE and 7 clients with Windows XP SP3 installed. Recently they have a problem sending emails. This affects all of the clients who each use either Outlook Express, Outlook and Thunderbird. They can receive emails with no problem but they cannot send. Their email addresses are - username@domain.local. I have checked with service provider and the person who manages their email and they assure me that there is no problem on their end. If they use a hotmail account there is no problem but their own business domain is not working. What should I be looking at to fix this problem?

Thank you!

Robert EhingerIT specialistAsked:
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Dan CraciunIT ConsultantCommented:
Check the firewall for a blocked port 25. Or see if their ISP has blocked port 25 (most do).

If so, switch to SSL and port 465.

Jerry MillsCommented:
ISP is blocking port 25 is first most likely problem.  Webmail will not be effected by blocked port 25.  Try alternative port 26, 487 or 587.
Where is the mail server? If it's hosted ask the hosting party to check the email ports. Another place to look is your own internet router. Did somebody change something just recently. Maybe some ports where blocked.
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Jerry MillsCommented:
You can test mail connection PORTS by using telnet from the command window.

1. Enter  "Telnet 72.X.X.X  25 " or 26 etc...

RESULT: ESMTP Exim 4.82  #2 Fri, 07 Feb 2014
12:29:36 -0500
220-   TruXXXX does not authorize the use of this system to transport unsolicited,
220    and/or bulk e-mail.

If you don't know the IP address use the nslookup command to find it:

Z:\> nslookup

> set type=mx
Server:  icscorpdc01.ics.local

Non-authoritative answer:    MX preference = 10, mail exchanger =    internet address = 72.x.x.x

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Robert EhingerIT specialistAuthor Commented:
I used telnet to check all the ports mentioned, 25, 26, 465, 487 and 587. I got the same result with all ports, "Connect failed."

The firewall on all clients is off. The firewall on the server is not running because ICS is not running.

When trying to send an email from a client using Thunderbired, no matter which port is used, the error is - "An error occurred while sending mail. The mail server responded, Relaying is administratively denied. Please verify that your email address is correct in your mail preferences and try again."

When sending from Windows Live Mail the error is similar - "Message could not be sent because the server rejected the senders email address. Server error - 550  Server response 550 Relaying is administratively denied."
Dan CraciunIT ConsultantCommented:
That usually happens when you try to send email from using

Check if the smtp server is from the same domain as the sender's address.

Robert EhingerIT specialistAuthor Commented:
It is. The thing is, all worked well until recently. An employee left the company and before he left he sent an email to all of his former customers and contacts. It appeared that he had set his computer to send these emails automatically and they were being sent repeatedly for several days. We were told to disconnect his computer and that the problem should be resolved but it isn't. The port the systems were set to use prior to me testing with other ports was 26. I have reset all clients to that port so we are back to our original settings.
Dan CraciunIT ConsultantCommented:
Is the email server Exchange? Or it's part of the hosting package (usually exim)?
Is the smtp server from the web host or from your ISP?

If the ex-employee managed to blacklist your IP on the server, you need the host to manually lift the block.
Check that you are not blacklisted.   Use your domain name to test blacklisting.

mxtoolbox has all tools you need to test mail servers.  

Also:  Check access using Telnet as per above - instructions at this url:

Robert EhingerIT specialistAuthor Commented:
When I checked using telnet I learned that the domain had been blocked by the hosting service because one of the business email accounts had been compromised. I was under the impression that the individual who manages the email and who set up this business with the hosting service had already contacted them. Apparently that was not the case. Once I contacted them and we reset all passwords the email was again functioning. I will award points to those who pointed me to using telnet as that is what finally helped resolve the issue.
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