>I guess I could have posted this on Rick's site. And in no way am I blaming the very ancient version of wwipstuff we are using because it still works.
>
>Of course everyone wants to blame the FoxPro VFP9 West-Wind wwIpstuff.dll business when we get this 451 error.
>
>451 451 4.7.0 Timeout waiting for client input (state 18).
>
>It's a FoxPro job running in a scheduler software that is similar to the Windows Scheduler. It sends emails to our SMTP server and then it goes to the Exchange server and out the door.
>
>The FoxPro email job works for 98 out of 100 other customers, but for the same 2 customers it fails every single time. And it takes 12 to 15 minutes to actually timeout. Because the job is on a ten minute timer schedule I had to split the FoxPro job up into two jobs - one for the successful emails and one for the ones that are going to fail.
>
>Now, the painful workaround is to resend the email with attachment directly through Outlook. And that works 100% of the time.
>
>I think the customer has some setting on their email server that is detecting that the email has been relayed or some other identifier.
>
>Of course, this is a job for IT, but because it's a FoxPro program now I have to get involved.
>
>Has anybody heard of this kind of problem?

Kind of a long shot but maybe a server is refusing connections because of protocol mismatch e.g. http://blog.ittoby.com/2014/07/why-schannel-eventid-36888-36874-occurs.html . If a server is recording those Event Log IDs around the time you're trying to send, it might be an issue.