I can't help, there is no single word "Failure" message on Xerox machines in english.
Connection failure, login failure, but certainly not just failure.
And you still have supplied nothing relevant to the issue at hand.
The 3 that work are irrelevant (Don't matter)
The ones that do not are in another location, meaning they are on a different LAN.
Since the printers are the same, and we have to assume the mail server is the same, then the only thing different is the location (or LAN).
So diagnose what is different between the LANS and don't assume the printer is at fault, because the DNS and Gateway you set on the printer is probably at fault.
If they were all using the same settings they would all work, since the LANs would be different, the likely issue is in DNS/Gateway, but since you fail to mention a single fault of any kind it is hardly worth troubleshooting because everything is just stab in the dark.
My computer doesn't work, why?
"Because the Power company is offline" could very well be the answer...
And since 3 machines work, but are not in the same location, they are totally irrelevant, they are on different LANs, All we know is the printers are fully capable of working just fine with the mail server you chose.
please should be informed that we have 5 Xerox 4250 ,we use Scan to Email features , it work very well in 3 machines , however it is not work in 2 which are insralled in remote site , all machines have the same mail setting configuration ,
can you please give me a solution .