Mysterious letter

One day my grandmother incidentally found a letter in an old handbook, describing the different artworks related to the place, she was born. The letter is signed Karen Blixen-Finecke.

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There is no connection what so ever between my family and the Blixen-Finecke or the Dinesen family. None the less the letter seems to be original, bearing Karen Blixens handwritten signature. As you can see the top of the letter is missing and it was found with no envelope.

The letter is of course written in Danish, and in an English translation it says something like:

Thank you for your letter. I would enjoy seeing Lawrence Durrell here, and I hope you and your husband will join him. Perhaps you will all have lunch with me when he returns? Please call me, Rungsted 797 between 9 and 11 to let me know when it would suit you.

I wish you a merry Christmas and send my kindest regards, to your husband also.

Yours truly,

Karen Blixen-Finecke

The questions are:

When precisely is this letter written?
To whom is it send?
Was it received?
Did Lawrence Durrell come for lunch?

Do you know? If you have some of the pieces for this intriguing puzzle, please let me know!