I can't say what has done it for you geedad, but can offer you a program if the problem returns.
It's called MailWasher (one of my favourites). I use it to check my email & delete the ones I don't want directly off the server, before I get OE to download the ones I do. It has a 'Preview' option that let's you read messages in plain text.
click here to read more & download the free version (one email account only).
If you have multiple email accounts click here to download the last free multi-account version. If you install it & require help with the settings just ask. G
PS - Some ISPs (like Tiscali) allow you to block messages from the specific email addresses. Check to see if your ISP/email provider gives you this facility. However, this cannot stop some spammers, who use below-the-belt methods, to send you their scum : (