Mail

"Hopefully, the mail finds you well" sounds unnatural.

To communicate the same idea, try:

"I hope my letter made it to you safely"

Good luck.

What exactly are you trying to say? Are you hoping the person likes the email? Or receives the email you are sending?

:)

Further to bagproductions comment:

If you are asking if they are well, and that you hope everything is okay when they receive the letter/ email then you can say:

"I hope that you are well upon reading this."

Although it is probably better to just say:

"I hope that you are well."

But its all down to your own preference/ writing style.

If you're referring to the mail making it the person you're sending it to, then I would say "I hope this letter makes to you safely" or "I hope this letter arrives safely"

A small correction to Pandamilk's comment:

"I hope this letter makes it to you safely"

(add an "it" after "makes")

The expression is "Hope this finds you well" and means the same as "I hope you are well". Yes you can use this expression.

I agree with liam. It might sound a little old-fashioned, but it's perfectly good English.