I did some further investigation and this was when I discovered the “Host Protected Area” (HPA) feature had been activated. At a guess, either the kernel or the disk itself activated this feature to prevent further damage to the troubled areas, but if you don’t know about it and don’t do deep enough research to find out about it, it could be easy to assume that the data is unrecoverable.

As the wikipedia article linked above mentions, a bit of hdparm magic (in my case thanks to sysrescuecd) and your entire disk will be visible again, leaving you free to attempt some data recovery (I used ddrescue and the errsize was only a few hundred K – haven’t found which files yet, so it’s likely data I don’t care about or never use!)

The following is the error message recieved (culprit email server / addresses replaced with example.org for obvious reasons – server2.alteredperspective.co.uk and apserver.co.uk are both aliases for the same machine – the sending email server, which is a valid listed server for the sending domain):

This is the mail system at host mail.apserver.co.uk.
>
> I’m sorry to have to inform you that your message could not
> be delivered to one or more recipients. It’s attached below.
>
> For further assistance, please send mail to postmaster.
>
> If you do so, please include this problem report. You can
> delete your own text from the attached returned message.
>
> The mail system
>
> : host
> mailserver.example.org[xxx.xxx.xxx.xxx] said: 554 Service
> unavailable; Client host [server2.alteredperspective.co.uk] blocked
> using
> Barracuda Reputation;
> http://www.barracudanetworks.com/reputation/?r=1&ip=81.101.61.148 (in
> reply
> to end of DATA command)

Now, 81.101.61.148 isn’t the IP address of server2.alteredperspective.co.uk – it is the IP address of my dads home connection, which being a home connection had been automatically added to many blacklists and is also liable to change randomly and without warning.

Basically, the receiving mail server is blocking emails from a valid listed server for the sending domain because the mail was originally sent directly to the valid listed server, which is not an open relay, on an authenticated connection for the sole reason that the originating sending client is on a home connection.

This is sooooo broken I just don’t know where to begin ranting.

I can’t remove the IP of the home connection – I tried that before – it goes straight back on there, or the IP changes, and we’ll hit it again a short while later.

The only thing I can do is to ask the recipient mail server admins to fix their server configuration.

You’ll also notice that for extra bonus points, the admins haven’t even changed the mail server admins email from the default ‘postmaster’ in the error message. I have a sneaking suspicion that the request to fix the mail server is going to end up in /dev/null (or just as effective, a postmaster folder that is never checked).

Update: I have now learned that a particular peice of software, Barracuda Spam Firewall, is a main perpetrator of this breakage of the email system. I highly recommend nobody uses it, and anyone who does stop using it immediately. The stupid breakage described above will cause far more false positives than blocked real spam and will frustrate your business contacts. Fortunately for my father, he has me to sort out this crap. Others may not be so lucky.