Emails are being lost (yet) again

[#1]

For the last week or so I have been having trouble with emails sent to me by a particular person sometimes failing to arrive. This afternoon he sent me an email which he also copied to my Google mail account - the Google copy arrived, the Plusnet one didn't. I've added all the headers from the Google copy to my ticket (23446256).
Looking at previous emails from the same source I have one from the same person on 19th November and another from a different person in the same organisation on 20th - both of which came through critical path boxes. I've lost emails from before those emails successfully arrived.
What is going on?

[#2]

I thought CS agents were supposed to be getting better! I've just had a response to my ticket:

Quote

Thank you for your support query, in order for us to investigate this matter further, Please advise us the date sent the time sent and the destination mailbox

I'd given them the full headers from the the Google copy which has all the information he'd asked for - what a plonker!

[#3]

Hi John,
Quite surprised as the CS analyst that replied to your ticket is normally very good.  He's passed your ticket through to Networks though, who will be able to investigate your issue.

[#4]

Edit: OK, checked the Exim logs and there's loads of errors for this email:

2007-11-21 21:05:45 your@email.address R=mysql_spamcore
T=local_spamfilter defer (145): Connection timed out:
error while writing to tmp/1195678845.H771673P16272.pih-sunmxcore12.plus.net

Basically it looks like one of the spam processes (Clam) is struggling to write information to a temporary file location. In layman's terms, the email's 'stuck' in one of the spam filters. I don't suspect this is going to be widespread but will have somebody look into into it none-the-less.

[#5]

Can you see other emails from the same person that are still AWOL? (Sorry can't give you precise date/times)
I've had a response to my ticket:

Quote

I have had a look into this for you and it appears the mail in question is in the "Filed" folder of you mailbox (xxx). You should be able to find this mail by using the "search" option in webmail and entering "xxx@yyy" as you're[sic] search criteria.

If I could get on to the portal I would add the following response to the ticket:
The email you have found is the Google copy which I copied across using IMAP - if you look at the headers you will see that it doesn't have the normal Plusnet "Envelope-to: " at the top. In fact it has "Delivered-To: xxx@gmail.com" - that might have been a clue!
Could someone add that to the ticket and return it for me please?
Edit: Finally managed to get on to the portal myself

[#6]

Bob,
If I turned off spam filtering - would it come out of the loop?

[#7]

The plot thickens! It would appear that this isn't Clam at all. It's Dspam locking up when it tries processing the mail. We've not seen this before TBH. Even if we try running the email through Dspam in isolation the same thing happenes so it looks like a bug within Dspam itself.
Good news is that we're due to be rolling an updated build out shortly. We've tested with this and it does seem to resolve the issue. Unfortunately, until this upgrade takes place there's no means of us pushing the email out. I don't think switching off spam or virus filtering would make any difference.
Oh, and to answer your first question, yes we can see other emails.

[#8]

Whatever was different about that email it's happened again today. The same person has sent me another email with updated versions of the plain text files attached - the Google copy has arrived and the PN copy is AWOL. I've posted the Google headers to the ticket.
What's the betting that it's stuck in the same loop!