I find that using a non-standard, but polite greeting in an email tends to be quite effective in getting people to actually read what you are writing. For instance, when writing to a group of people, it is quite common (in New Zealand) to write:
To whom it may concern,
or, as has been mentioned:
But I tend to write something off carte like (assuming that I worked at British Telecom–which I don't):
Dear BT Person,
I have found that this unusual approach—which also feels less impersonal—can be more likely to garner an audience.
But where I currently work, we have a tool to address everyone individually, we just leave a placeholder where their name is, so it will say:
Dear Mr. Smith,
Which I think is probably the best way to get it done if it is convenient.