Though when these problems crop up MS fixes them pretty fast

I dunno, I don't keep up on it but I have never heard of anyone who uses web-based mail get virii from it.

[Link]

Some email clients automatically open attachments when you open the mail. The attachment could contain scripts, code, macros with viruses or spyware.

Also if your mail client is set up to automatically display HTML in emails I can imagine situations where the HTML contains or links to malware that would get run when you open it. I know some people who set their mail client to display only plain text for that reason. This could happen either with web-based email or "real" email.

Apart from the obvious ones, two standard recommendations for avoiding viruses are

1: NEVER run Microsoft Outlook
2: NEVER run Internet Explorer

[Link]

I don't know if any similarly exploitable flaws have been found in e.g. Thunderbird, but I'd at least make sure it doesn't show HTML content by default.

[Link]

Outlook may still be willing to execute in HTML mail, which has potential problems. Future versions of Outlook will use the Microsoft Word HTML rendering engine instead of Internet Explorer's, which is not exactly a step forward for any perspective, including security.

Another issue is images. If an HTML email contains a reference to an image on the Internet then the sender can track when you read the email. Spammers love this.

In general I try to junk obvious stuff without even previewing it. When in doubt I look at the message source with command/alt-U.

[Link]

Thunderbird also has a checkbox to enable in incoming messages. I always operate with turned OFF, i.e. this box is unchecked.

[Link]