CmdLine
The admin name is hard coded & not likely to ever change in sme server for the forseeable future, it has been that way since inception of sme server back in 1999 or so. If you lodge a new feature request (NFR), which is a good idea to do, then even if someone starts work on it now, the feature will not get into sme server until at least v9.1, which is probably a year or more away (minimally & if the NFR is adopted).
You could use procmail or mailsorting (contrib) etc to filter the admin mail, so that system messages get forwarded to another user, say sysadmin@mydomain.
If external incoming admin@ mail is the main concern, you could configure external DNS/zone records to forward admin@mydomain to another email address.
....but that's a temporary solution and the new virtual domain user receives system email. I was hoping somebody had a perminent solution to this problem.
Why do you feel that is a temporary solution ? The situation described was a temporary one until they stopped using the admin mail account, but it does not make the fix a temporary one.
You can permanently give your sme server a new main domain name of abc.dyndns.org or mydomain2.com (or whatever valid domain name you prefer), then create a virtual domain in the Domains panel, for your current main domain name, say mydomain.com
Then create the pseudonym admin@mydomain.com which forwards to whichever normal user currently receives the businesses administrative type admin mail.
System/root mail etc will automatically go to admin@abc.dyndns.org (or whichever domain you select as the main server domain), & can then be forwarded "as usual" to the sysadmin user via the User panel in server manager.
All other email messages will go to the normal users, as they are valid users for the main domain & the virtual domain.
Ultimately the best option will be to discontinue the use of admin for business adminstrative mail, as sme server is not likely to change in the immediate & forseeable future.
You could offer to pay someone to rewrite the code to make the system mail account configurable, & hopefully someone would be willing to do the coding. That's how many new features have made their way into sme code, by corporate sponsorship.