To my greatest granddaughter

It was addressed to me, Marie Jones VII,
At 5949 Library Drive,
With the return address obscured with a water stain
And the postmark 2/20/1799,
The seventh anniversary of the postal service.
As to who wrote it?
Marie Jones VI may know,
And I envision the letter should start
“To my greatest granddaughter”
Since that’s how I intend to write my own.
It said:

I’m writing you this letter in 1799,
Thrilling over the end of the century
The new country, the possibilities
Of everybody learning to write,
Everybody writing letters every day.
Although you are not born yet then-
How can you be-
I wrote it in my will to keep the family names
And family homes intact;
To pass this down across the generations.
You will not know me now; I have signed as
“Madam Marie,”
But when you know me you will know your ancestry.
And write a letter to the 10th generation of me;
To write is to make history.