Pretty common question but one that requires a good and thorough collection of answers.
We've all been there, the email format doesn't match anyone else at the company, you've tried every name possible. The phone number you have goes to a VM that doesn't state the name - Office line never gets picked up since no-one is working in their office - etc....
At what point do you give up on contact information and move on?
Personally, we leverage ZoomInfo and other random sources to find numbers, emails, and what have you, but when it comes to getting the person to open your email (sometimes blocked by proofpoint or other security blankets) or picking up a phone (not to mention calling the right number) sometimes it gets tricky and I find myself having to give up for the sake of moving to the next prospect.