“They just contacted me out of the blue.”
You just started a new job. Your friend asks you how you found it. You tell her that a recruiting company contacted you unexpectedly a few months ago.
They just contacted me out of the blue.
To "contact" someone means to call, email, or send a letter to them. Those words are all specific, but "contact" can mean all three.
One of the many ways to use the word "just" is to talk about something that happens suddenly:
He was there, and then he just vanished.
It just stopped working all of a sudden.
This idiom means ‘suddenly’ or ‘unexpectedly'.
And then out of the blue she decided she wanted to be a nurse instead.
He was doing fine and then out of the blue started getting these severe pains.