At this time i have 3 Servers with GW7SP3HP1:
Server1: Primd(MTA with primary domain), WORKD(secondary domain with
postoffices), POST1, POST2, POSt3 (users postoffices)

Server2: INTERD(MTA(secondary domain) with GWIA, WEBACCESS)

SERVER3: FILD(MTA(secondary domain) with POS4

Such order of transition will be correct:
Step1: Upgrade from GW7 to GW8 Server1 (Primary doamin, secondary

After this step Server2 and Serever3 - with GW7, Server-1 - with GW8
I Ask: GWEbaccess from Server2 will be work with GW8 on the Server1 ?
wait 2 days.

Step2: Upgrade Server3 from GW7 to GW8 (mta+poa)
wait 2 days.

Step3: Upgrade Server2 from GW7 to GW8 (mta, gwia, gwwebaccess)