Having sent a campaign to myself and viewing the mail in Mac Mail (v4.3) via the default mail viewer (all images are shown, none blocked), but the open is not recorded.
Is this normal?
I haven't double-clicked on the mail nor any of the links, but I was under the impression that even using this preview option an 'open' rate would be registered.
Can you confirm please?
Yes, as long as the tracking image is downloaded the open will be recorded - see http://help.campaignmonitor.com/topic.aspx?t=89
Is it possible your mail server is blocking 'web bugs' or tracking images?