The only problem shown here is that you are accepting mails for local (non-virtual) recipients, and there's a conflict regarding the www-data user. See the following lines (they are cut so the full maildir folder where it's trying to save the mail isn't shown):
Code:
Mar 10 14:30:03 server postfix/local[22676]: B350E33C31E: to=<www-data@server.witchermod.org>, orig_to=<www-data>, relay=loc$
Mar 10 14:40:03 server postfix/local[23600]: warning: maildir access problem for UID/GID=33/33: create maildir file /var/www$
Basically, "www-data@server.witchermod.org" is detected as a local account because "server.witchermod.org" is your mail host name (mydomain in the main.cf) and "www-data" is an existing user in the machine. Then, it tries to deliver to the user's $HOME/Maildir maildir, that in this case maps to "/var/www/Maildir", a folder that cannot be created by the www-data user, and hence the error.
That said, solving this is as simple as changing the "mydomain" setup variable to "server.witchermod.org.local" and restarting postfix. Then add "server.witchermod.org" as a normal (sub)domain in ispcp and setup any mail accounts you want from there.
Regarding the authentication problems, there is nothing wrong shown in this log. Anyway, I suspect that you are hitting
this problem regarding Outlook 2010 and the NTLM authentication failures (the solution is explained there).