Correct, "mail" is a reserved account name (one of many). This is an expensive mistake by your client
I strongly disagree. It's a design limitation in the SME Server out of the box (but easily fixable). Suggesting that the fix is to reprint stationery won't win friends...
and has no workaround, AFAIK.
There are lots of workarounds, and it should also be raised as a bug. The quick hack workaround is:
echo fred > ~alias/.qmail-mail
While this works, it won't be kept across a backup/restore. But it's a useful interim measure until it's fixed properly.
The proper fix is to allow 'system' accounts to be managed as for normal accounts in the pseudonyms panel. At the moment there is code which gives all 'system' account mail to 'admin'. That should be configurable on a per-account basis, defaulting to admin.