Eliminated some volatile qualifiers.

Converted active client counter to a protected (thread-safe) integer.

Change active node count to a protected (thread-safe) integer.

for password" and the user enters a unknown user alias/id.

The connect timeout is now configurable in sbbs.ini [Mail] ConnectTimeout
(default = 30 seconds), set to 0 for blocking connections (and OS-default
timeout).

- if configured max recipients = 0 means unlimited (for all users)
- max recipients limit is applied to pending send emails (non-M-exempt users)
- M-restricted users can not receive unauthenticated SMTP mail messages
- Introduced inbox msg limit (for non-M-exempt users) with sbbs.ini [Mail]
  MaxMsgsWaiting value (default: 100), 0 = unlimited

are now executed with the node's global object as the scope of the script.

being called for non-mutex-protected lists causing exceptions on Windows.

destination server: if an MX server connection fails, "negative cache"
the failure for that iteration of the sending loop so we don't attempt to
reconnect to the same server(s) repeatedly for the same iteration (and let
other mail get out more quickly).

"max clients" value rather to determine the size of the bar rather than the
configured max clients value of the web server (copy/paste bug).

"active_clients" counter which has been seen to "go negative" under high web
server utilization (on Linux and Windows).

(interlocked/atomic) integer variables.

to the cterminal structure to permit thread safety.

Various conio functions are now pointers in the cterm structure so they
can be replaced by Something Else.

thread-safe module.

supported, doesn't always work correctly (e.g. it's just a "hint").