Here is some good business advice for both colleagues and clientele alike: Put something in your email subject line whenever you send something. And and don't make it "For Phil" or "Attn: Phil."
Getting an email with nothing in the subject line is a minor annoyance. But it can also be expensive. Here's why: 2 weeks or two years after an email has been sent, it may need to be retrieved for a variety of reasons. It could be a phone number, the confirmation of a the date of a showing, or one of a thousand other bits of needed details that can't be sifted out of the enormous inboxes we have without some sort of detail, such as an address or other specific.
The way cloud computing is becoming more prevalant, I can search emails on my smartphone. This is a huge gamechanger-IF, and think of the GIGO principle here, IF I have the necessary word, address or specific to index. If I am searching for an email one of my clients or agents sent me for example, I could have years worth of correspondence to look through if all the subject lines were blank. You can search body text, but if 50 emails come back with (no subject) in the line, time and money are lost.
The subject line is there for a reason. Use it.