Nearly everyone has business contacts, former colleagues, and even friends they fall out of touch with. These are people who may think highly of you, and the blame for not being in touch may go both ways, but for whatever reason, you stopped communicating.
After a certain amount of time, getting in touch with a lapsed contact for professional reasons can be awkward. Sending an email that basically says, "Hey, I know we haven't talked in a while but can you do this for me?" isn't comfortable. It's also less likely to produce the result you hope for.
A lapsed contact might still give you a reference or make an introduction, but it's also possible they won't get to it as quickly as they would for an active friend.
However, the holidays offer a chance to reconnect with people at a time when you don't need them. It's a way to reach out, say hello, and warm up a contact that you might need down the line.
What should you do?
Go through your contacts and make a list of people who you have not spoken to in a while. Reach out to each one with a personal email, direct message, or even a text if that's how you previously communicated.
Apologize for falling out of touch and offer a short update on how you are doing. Make sure you ask a personal question about how their life has been. It doesn't have to be a long letter -- just touch base and show an honest interest in the other person.
It's also important that if the person responds you answer in a timely fashion. This is about rebuilding bonds and reconnecting on a personal level before anything else.
How does this help?
You want your network to be an organic one -- people you connect with on a personal level that will want to help you professionally. Work on building your relationships back to a point where the people in your network think fondly of you and feel like you're an active friend.
Once you reconnect, make an effort to stay in touch. That doesn't have to be overly formal, but you don't want to fall into the habit of letting contacts grow cold and then warming them up every holiday season.
Even if you have to make a schedule or put notes in your calendar, check in with people a few times a year. Send a note on their birthday or acknowledge shared milestones. Keep in touch in a way that feels appropriate for the relationship.
This can have clear professional benefits if you need something from someone in your network. It can also personally benefit you as you improve friendships and reconnect with people from your past.