Domestic
Code - Definition

Y -- Address and 5-digit zip code match
Z -- 5-digit zip code matches only
A -- Address matches only
N -- Neither Address nor zip code match
X -- Address and 9-digit zip code match
W -- 9-digit zip code matches only
U -- Address info not verified for Domestic transaction. Returned if the US bank does not support non-US AVS or if the AVS in a US bank is not functioning properly.
R -- Retry - System unavailable
S -- Service not supported
E -- Address verification is not allowed for card type

International
Code - Definition

G -- Global non-AVS participant
B -- Address matches only
C -- Address and postal code do not match
D or F -- Address and postal code match (F is for the UK)
I -- Address information not verified for international transaction(s)
M -- Address and postal code match
P -- Postal code matches only