YOU SAID:

That was why he was so surprised to receive this letter

INTO JAPANESE

それで彼はこの手紙を受け取ってびっくりしました

BACK INTO ENGLISH

So he received this letter and was surprised

INTO JAPANESE

それで彼はこの手紙を受け取って驚いた

BACK INTO ENGLISH

So he was surprised to receive this letter

INTO JAPANESE

だから彼はこの手紙を受け取って驚いた

BACK INTO ENGLISH

So he was surprised to receive this letter