How should I communicate with customers I haven’t contacted for a long time?

First of all, confirm the customer status through various channels, such as whether he is still in the original position, whether he is still working on your product, etc.; in this way, if the customer is no longer responsible for your product, you can still ask him to recommend it. Give your product to the current person in charge; secondly, think about how to explain to customers that you have not contacted them for such a long time. Of course, you can also tell a little lie, such as being assigned to work on a project in another place, being sent to a foreign office, etc. However, it is better to try to contact the customer from time to time. You can find an entry point, such as holidays, customer birthdays, or what new products you recommend to customers, etc. But customers probably won’t care too much, so don’t worry too much.