Very slow at the best of times
As we have limited mobile signal at work, my wife, who works at an isolated doctor's site, used to occasionally send me an email to get milk on the way home, or more importantly pick up a child.
The mails from the NHS are always delayed by an hour or two, but the worst we have seen is 9 days - 7 within the NHS servers and then 2 when my companies system threw a wobbly (presumably as the email was so old). For important and time critical communication they have to revert to printing the email and faxing an image!