This static NAT statement is incorrect:
static (inside,outside) tcp 207.x.x.x 873 192.168.1.20 873 netmask 255.255.255.255
It should say:
static (inside,outside) tcp interface 873 192.168.1.20 873 netmask 255.255.255.255
I am assuming that when you say 72.x.x.x, you mean your ASA outside interface ip address, right?
Also, access-list 100 needs to allow that connection:
access-list 100 extended permit tcp host 207.x.x.x interface outside eq 873
Hope that helps.