One of my sub-account holders is being moved to BT Mail soon but I'm still on Yahoo. Is that possible - seems strange? Do I need to do anything to prepare for this? I know that there are mail client settings to adjust when the changeover happens but I haven't gifted this account to the holder - would that be a good idea? Why is BT email SO complicated?
The email addresses are totally independent so it is perfectly possible for them to be on different platforms. The move is being made individually so many customers have emails on both platforms until all are changed over.
As long as any client is using the correct servers (mail.btinternet.com) then no intervention is necessary.
Gifting has no impact on the changeover, entirely up to you if you wish to pass the management of the account to someone else.
See link regarding changing settings prior to the migration.