Connection was dropped by remote host

We have a business partner that uses google apps.  Recently we changed the IP address of our email server and now they get an error "Connection was dropped by remote host" when they try to send us email.  They are the only ones that are getting this error.  Could it be something on our end causing this? How can I determine which end the error is at?
Pancomp60Information Systems ManagerAsked:
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TravisTCommented:
You need to check your DNS settings to make sure they have propagated correctly after changing your IP address.

Once that is done, you and they, need to run a DIG or NSLOOKUP from each location to make sure the same data is returned for the MX record and IP.  It may just be that their machine has cached the IP address of the previous MX record and it will stay that way until either (a) the requirements are met for the old/new DNS record you have set (timeouts, etc..) or until they force a fresh new DNS lookup of the MX record.

Travis

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buildingkickCommented:
I need a little more info about the end users environment - a quick and dirty guess is that they may not have the updated DNS records (with the new IP address) in their system which may cause it to not resolve properly until the records are updated.  Again, depending on the environment, a simple flush of the DNS or reboot could solve this problem if they are the only ones having an issue.
Barry GillChief of StaffCommented:
conection dropped by host tells me that the server they are trying to send to does not accept port 25 connections. is the old IP yours or has it had it's smtp listener disabled?

if you are receiving from everywhere else, ask them to raise a trouble ticket with their provider as this fault is on their side entirely.

Have you checked your firewall rules where a block googl IP's rule may have kicked in? (sometimes these things get created on one server and you move from one to another and forget about that old rule - though I would not think this is likely, but worth checkin out)
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Pancomp60Information Systems ManagerAuthor Commented:
buildingkick: wrote:
I need a little more info about the end users environment

They are using Google Apps as their email system, so they do not have any control over their MX records; it is entirely hosted by google. I will ask them to check the dns record on a local machine to see what they have for our domain.
TravisTCommented:
Not their MX records, yours. Their MX records only affects their incoming mail.  By guess is by now, any DNS issue, has been cleared up since the new zone data probably propagated by now.
Barry GillChief of StaffCommented:
exactly. so the big question is WHERE are they trying to send mail.
Have you checked your firewall yet?
Pancomp60Information Systems ManagerAuthor Commented:
I am working with our provider to have them confirm that our DNS records and our MX records are accurate, and that the individual's address is not being blocked by the firewall.
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