Many of us have business cards from old acquaintances we've met along the way. These contacts might not have been "sales ready" when you met them so you may have lost touch.
A strategic way to build business is to stay connected with these old contacts by sharing educational information. An email newsletter is an ideal way to do this since it keeps you top-of-mind while positioning your IT company as an expert.
Not all of your contacts will remember who you are or where you met, just as you might not remember all of those people you have met at networking events. If you simply started sending a newsletter to these people without any context, they might label it as spam, which could cause blacklisting or other problems.
To provide this context in your first newsletter, say something like this in the intro section (tweak as you see fit):
Hi <firstname>, we had exchanged business cards a while back. I'm reaching out to our old contacts and I thought you might be interested in these current IT issues that can affect your organization.
I'd love to reconnect over lunch sometime,
<your signature info>
The benefit of using an opening like this is that you remind people that you have met them at some point and that you are not sending them a message out of the blue.
Plus, the bit about lunch is another way to refresh a relationship in case someone doesn't remember you. It can help start a dialog to see if they could use your services or provide a referral to someone who does.