All seems to be working well with ISPConfig - but I have noticed an odd thing with the webmail login. https://www.domain.com:81/webmail fails to do anything but https://www.domain.com:81/webmail/ works. I thought that apache added the missing / if it was needed, so why not here? I've also noticed that on one of the hosted websites, there is a directory whose index page is index.php but going to that directory doesn't open the index page, even thought index.php is listed as an index file name. I wonder if these two are linked problems. Whether or not, I'd appreciate any suggestions!
I think you may have identified the problem. The actual address I'm using is https://hosting.hairydog.co.uk:81/webmail There is no site at http://hosting.hairydog.co.uk yet, just the default index.html The plan is to have a completely different site at http://hairydog.co.uk and the same at http://www.hairydog.co.uk (though the DNS for that points somewhere else at present) The ServerName was set as hairydog.co.uk but I've changed it to hosting.hairydog.co.uk - and that seems to have fixed the problem. Thank you for your help.