SBS2003 - problems sending emails with attachments

server is SBS2003 standard, all patched and up to date including SP2 for Exchange 2003.

smtp traffic had been flowing normally, but we now have an issue with sending messages that have attachments - of any size.

have dbl-checked the message delivery options and the smtp server options and there are no restrictions on message size.

messages without attachments get sent fine.

messages with attachments sit in the outbound queue with 'retry' displayed.

totally stumped, all suggestions gratefully receved!
SamTinleyAsked:
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SamTinleyConnect With a Mentor Author Commented:
after cheking everything else, turns out it was a fault with the router - changed that, mailflow all ok again
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Glen KnightCommented:
uninstall any antivirus/SPAM software you have on the server and then reboot? Does this allow you to send attachments?

If so, re-install the software and see if it still works.

It could be a corrupt install.
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SaoiCommented:
Can you send files internally?

Check the MTU size you can send by using the ping test as shown in this KB: http://support.microsoft.com/kb/314825/en-us

Run the test from the SBS server. If it turns out to be an MTU issue you may need to adjust your network switch/router/firewall.
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Glen KnightCommented:
I would be suprised if it was the MTU if this was working but has now stopped.
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SamTinleyConnect With a Mentor Author Commented:
looking in the Exchange queue manager, it says that "The connection was dropped by the remote host".

how can I find out why this is happening?

it appears to be failrly random - i.e., most mail is flowing outbound ok, just some messages sit in the queues

I've checked mxtoolbox.com and the public IP is not in any blacklists, there is a PTR record that matches the FQDN used by the server.
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Glen KnightCommented:
Using this guide here: http://support.microsoft.com/kb/153119 telnet to the server causing the problems on port 25.

When you use the ehlo command use your domain, se ehlo domainname.com and then in the mail from use a valid email address on your server and the rcpt to use a valid address on the recipient server.
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SamTinleyConnect With a Mentor Author Commented:
thanks, but smtp telnet test isn't much of a help, unless you know how to add attachments doing that?

as stated, messages without attachments get sent fine, messages with attachments sit in the smtp outbound queues.

have tried disabling A/v & anti-spam services, no difference.

have re-run the ICW, no difference.

have dbl-checkd and public IP not currently in any spam RBL's, and has matching PTR record for the fqdn used by the server.
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Glen KnightCommented:
Then it can only be a problem at the recieving server end, I would suggest you ask their IT bods to check the logs and see why the attachments are being stripped.
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SamTinleyAuthor Commented:
that's a fairly sweeping statement demazter, based on a relatively small amount of information!

if it was a single recipient domain that the client had a problem with I would probably be inclined to agree with you. but the fact that it's an issue trying to send any attachment, by any user, to any domain suggests otherwise.

there could be multiple other reasons local to the client's network that might be the problem - issues with LAN hardware such as switches/router, problems with the quality of the ADSL service, problems on the server itself - faulty nic? code fault in the tcp/ip stack? broken smtp virtual server? hidden malware infection?

the help I need here is with troubleshooting steps to identify exactly where the problem is.
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SamTinleyAuthor Commented:
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