A trend is a movement either going up or going down. A trend is not a steady, straight line. It is a change, and in the email marketing world, like in most others, it's either a change for better or worse.

Trends are meaningless, however, if you don't spot them and act upon them in a timely manner. Trends can be positive, such as if your forward-to-a-friends are increasing. Or it could be a negative trend,such as if your open rates are decreasing. In the first case, you'd want to figure out why more people were forwarding your emails so you could do more of the same. In the second case, you'd want to find out why fewer people were compelled to open your email.

When you're in the email marketing business, you're no doubt paying attention to your email marketing metrics with each send. But be sure to look at your metrics over time too. That's how you spot trends. If you're only looking at the numbers for a particular campaign or time period, say a month's worth, you're unlikely to spot those gradual changes we recognize as trends.

Below are a few things you want to watch for and act upon over time:

If your numbers are moving in the wrong direction, analyze what you're doing that is causing the bad trend and correct it right away. And wrong doesn't always mean down. Bounce rates, unsubscribes and spam complaints are numbers you don't want increasing. You should also consider your audience size, if you're making an effort to have quality over quantity.

When you spot a trend, or even a sudden change, look at what's changed within your email marketing program to cause the shift. Did you change your frequency? It could be that some subscribers are hearing from you more often so now they're opting out. Did you change your From name? Your messaging? Your template? And these could all be positives too! It might be that changing your From name increased recognition or interest at the inbox, so your open rates reflect a positive upward trend.

When you look at bounce rates, these should be very, very low. And bounce rates are usually less of a trend and more of a one-time red flag. If your bounce rate suddenly goes up, stop. Look at what you did differently for that campaign. Did you use a new, image-heavy design? Were there words that triggered spam filters?

Sudden changes can be the result of a one-time action internally at your company, that's outside of your email marketing team. Maybe an over-zealous sales team added a bunch of email addresses to your list after collecting business cards at a trade show...but they didn't exactly get permission for your company to email all those people.

If your email deliverability rate is trending downward, that could be a sign of a problem outside of your company. Your ESP could be having issues with ISPs, for example. Or it could be internal. Email deliverability best practices shift and change regularly.