In addition to your excellent list of programs nduncan, could I strongly recommend using Mailwasher to safely view the contents of your e-mails and be able to quickly and easily delete the unwanted ones off your server, BEFORE they are downloaded into your computer.
It can handle a number of different e-mail accounts simultaneously and does not allow for attachments to be opened, as it displays only in plain text … but it does allow you to view and check the headers, if required.
An easy to use program which, in its basic form, is free to use. For a very reasonable amount it can be upgraded to Mailwasher Pro, giving you the option to report Spam and Bogus mails to SpamCop who in turn send a report to the ISPs responsible for allowing them to be sent through their systems. Two excellent programs that have kept my system clean and which are making it more difficult for the spammers ... slowly but surely helping to decrease the amount of rubbish which is being sent.