Hopefully, the check is in the mail.
vs.
I hope the check is in the mail.
In this example, the use of "hopefully" is incorrect. A word that ends in -ly is an adverb and modifies a verb. "Hopefully" cannot modify "is."
If you can substitute "I hope" for "hopefully," you shouldn't use "hopefully."
Confused? Just delete "hopefully" and revise the sentence.
