Downtime wont be more than 30 minutes for moving email service on Linux but you will need to manage email accounts from a different control panel so that would be lil inconvenient for you but you will get highly reliable solution.
Some of our existing customers already have such service with us and thats why they never bother to come on the forum
my tone sounds harsh as I know I have given more than 100% in getting problems sorted with 87.117.201.122 but now only webmail problem is left so you should at least appreciate our efforts in making server stable for all other services. Only webmail service has got problems with it which is due to sharing of application pool ( our windows system admins have said so ). MailEnable is sharing application pool with default application pool of IIS Web Server so webmail breaks when you change ASP version from the control panel. This seems to be a huge bug in hostingcontroller and I am not going to spare them on Monday.