What about CAPS in the SUBJECT: Field?

E-mail etiquette suggests that full caps should not be used as it gives the impression that you are shouting. Does this apply to the Subject: line?

Of course there are exceptions to every rule, however in general, caps are shouting and if used in the Subject: field can be construed as such ("bringing attention to" by shouting). Or worse yet, you could be misidentified as a spammer because most spammers don't understand the nuances of case.

If you want to bring attention, it would probably be better to structure your Subject: field to include both caps and small case such as:

Subject: FOLLOW UP: Previous E-mail Subject

Subject: REMINDER: Tomorrow's Meeting

Now, one could assume you were shouting if:

Subject: WHERE'S MY ANSWER?

Subject: DID YOU GET MY E-MAIL!!!!!

See, it's all in the words you choose and how you choose to use them that can determine if you will be perceived as yelling.

So it is clear by the first examples that you can use caps to draw attention in the Subject: field without giving a negative perception even before your e-mail is opened.