Which means in the case of this particular email, where it's one big image, the only thing a recipient will see is...an unsubscribe message! Not really what they're going for, especially as an increasing proportion of people, weighed down with too many emails, are unsubscribing from email marketing lists these days.
This situation could have been avoided if they'd sent both text AND images in the massage. Whilst the images will still be initially blocked, you'll still get the core of the message across, allowing the recipient to decide if they'll download the images - and see the message in all its glory, just as the hard working marketer intended.
So in the "zero budget" vein of making sure everything you do is optimised, this is a cautionary tale of how not to do email marketing.
I'd strongly advise against having too much of your message in images - especially if you're sending to a business prospect or customer where the majority of people are running Office software. Yes, some people will see it as you intended, but a distressingly large proportion of people will just ignore your message, or worse, click that easy to spot unsubscribe link.