Response from NSS - Any GP, including Sessional GPs, are entitled to an NHSmail account. The issue is whether they should be attached to the practice they work in or not. I would suggest that if they are likely to work in a practice for 3 months or more they should be attached to the practice and if they move to another practice they are marked as a leaver from that practice and then added to the next by the practice admins. This would need to be done by your local administrator. If they are only working for a week here or there, they should float within the Board (not attached to anything except GGC Board).
To get an NHS Mail account a Sessional GP should phone DAISY, the IT Company NHS Greater Glasgow and Clyde use to support their systems, on 0344 863 1244 and log a call. The operator will take the GP through a series of questions, including which Health Board they are hosted by, take contact details, and then the account will be set up.