A. Below is a list of the service packs available:

Exchange 5.5

Service Pack 4 from http://www.microsoft.com/exchange/downloads/sp4.htm

Service Pack 3 fromĀ 

ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/eng/exchg5.5/sp3/server

Hotfixies for SP3 from ftp://ftp.microsoft.com//bussys/exchange/exchange-public/fixes/eng/exchg5.5/postsp3

Service Pack 2 from ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/Eng/Exchg5.5/Sp2/Server/

Files to download:

SP2_550A.EXE Server update for Alpha
SP2_550I.EXE Server update for Intel
SP2_55CA.EXE Chat server update for Alpha
SP2_55CI.EXE Chat server update for Intel
SP2_55DC.EXE Documentation
SP2_55FO.EXE HTML Form ConverterĀ 
SP2_55SS.EXE Server support files (cluster,KMS,etc)
SP2_55XA.EXE Exchange connector installation(Alpha)
SP2_55XI.EXE Exchange connector installation(Intel)
SP2S550A.EXE Server symbols for Alpha
SP2S550I.EXE Server symbols for Intel
SP2S55CA.EXE Chat server symbols for Alpha
SP2S55CI.EXE Chat server symbols for Intel
SP2_55RE.EXE Readme and HTML file

Service Pack 1 from ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/Eng/Exchg5.5/SP1/Server/

Files to download:

SP1_550A.EXE Server update for Alpha
SP1_550I.EXE Server update for Intel
SP1_55CA.EXE Chat server update for Alpha
SP1_55CI.EXE Chat server update for Intel
SP1_55DC.EXE Documentation
SP1_55FO.EXE HTML Form Converter
SP1_55SS.EXE Server support files (cluster,KMS,etc)
SP1_55XC.EXE Exchange connector installation
SP1S550A.EXE Server symbols for Alpha
SP1S550I.EXE Server symbols for Intel
SP1S55CA.EXE Chat server symbols for Alpha
SP1S55CI.EXE Chat server symbols for Intel
SP1_55RE.EXE Readme and HTML file

Hotfixes post Service Pack 1

PSP1STRI.EXE Store Fix

Exchange 5.0

Service Pack 1 from ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/Eng/Exchg5.0/Sp1/Server/

Files to download:

SP1_500A.EXE Server update for Alpha
SP1_500I.EXE Server update for Inter
SP1S500A.EXE Server symbols for Alpha
SP1S500I.EXE Server symbols for Intel

Service Pack 2 from ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/Eng/Exchg5.0/Sp2/Server/

Files to download:

SP2_500A.EXE Server update for Alpha
SP2_500I.EXE Server update for Inter
SP2S500A.EXE Server symbols for Alpha
SP2S500I.EXE Server symbols for Intel