GSI is the Government Secure Intranet, which basically covers most major departments and shares a common security level against external access. Emails between GSI sites are sent only within government systems and so never go over the internet where they could be intercepted.
GSX is the Government Secure Xtranet I believe. This is smaller government agencies who can’t afford the massive costs involved in being on GSI. They have to achieve a certain standard of security to qualify and email between GSX sites and other GSX or GSI sites is sent via GSI on dedicated connections, so once more it doesn’t go over the internet.
You will notice DWP’s email addresses are all dwp.gsi.gov.uk as default, so relevant systems will identify them and send emails via secure channels. We could also send things to DWP at dwp.gov.uk, but relevant systems would not recognise the security level then and would send via the internet.
Same applies for Scotland LAs on GSX, if the address sent with their emails is .gsx.gov.uk DWP can email them, but if their default sent on emails from the LA is .gov.uk DWP won’t deal with them this way, as any reply goes via the internet and could be intercepted.
DWP were going to be looking at secure email options for other LAs, but I don’t know how that’s going. We’ll all find out in time if they can arrange it and still keep their own GSI classification, as that is a standard they must meet and do not set.
.
