I accidentally opened a malicious email with my iPhone. Are there any specific precautions/actions I should take?

There is an antivirus app in Apple's ios app store. It is from Intego. It will not scan your ios device, but it will scan the attachment that you found on your email and if it is malicious then the scan should identify it and give you the option to safely delete or quarantine it. You have to use your finger or a stylus to select what you want it to scan. You just press down on what you want it to scan and don't let go, and then it launches and quickly scans that one item. This is useful to make sure you don't spread it to other people more so than protecting your own device, I've heard, as the ios devices are already fairly safe.

I have the Intego app and can vouch that it is easy to use. I scanned a few pdf files I saved on my iPhone 4 and they were clean.

If you are worried about your Mac, I recommend trying ESET antivirus for Mac. It is light on resources and does not cause any problems, whereas most other antivirus software programs are notorious for causing problems on the Mac. I've had ESET since June on my iMac and haven't had any problems, and it does not slow down my Mac or hog resources.

I don't know, but if they have your email address, they can sell it to spammers. But I think we're all smart enough to deal with spammers in our own way. After all, there shouldn't be too many users today who fall for Colonel Juan's email saying he has $50,000,000 he needs to move out of his country and would you help.

If you're worried about a virus, there are none on Apple devices/computers. Device apps are sandboxed (and now, applications from the Apple Mac App Store are/will be also). This means one virus cannot sabotage another app's space. However, the web site may now have your email address and other info. They might try to use that in some way.

The only time you need to worry about a virus on the mac is when you have a dual boot setup where you can boot into windows. There you definitely need antivirus. The other situation is when an email contains an infected attachment and you want to avoid forwarding it to other people . But your mac will be safe. Other than that, buying antivirus for the mac is a waste of money.

As someone who accidentally forwarded a virus to someone from a PC years ago, I wanted to reduce the chances that I might do that from even a relatively safe Mac. So, I installed ESET. Considering the fact that ESET does not cause any problems, I don't consider that a waste of money. And considering that the original poster says he is worried, this might provide some peace of mind.

Good point.