It's a more imaginative way of saying "I hope you are well." It is a pleasant way to begin the letter. I disagree with the comment saying that the person writing doesn't really care. It's the same kind of poetic device you use when you say something like "I hope this day brings you happiness." Days don't actually bring anything. Things happen during a day, but the day doesn't bring them. Similarly, emails don't actually "find" anything.

Really it’s just an introductory sentence. The person writing doesn’t really care whether you are well or not! 😂

This email "finds" you when you read it. This is referring to your overall mood or state of being when reading the message. This is an older expression and was more common in the days of letter writing. At that time, a message could take weeks or even months to reach its intended recipient. Similar expressions I hope you are well/are doing well I hope everything is going well for you

it means you will be healthy and in good mood opening the letter