The Maildir is a structure is defined in http://www.qmail.org/man/man5/maildir.html and the version used in DreamHost is the one expanded by http://www.courier-mta.org/imap/README.maildirquota.html
Quick and dirty: ~/Maildir holds your inbox. It uses 3 directories: new for messages recently arrived and were never read by anything (were thing applies to software rather than people... that is, if your mail program (Thunderbird, Outlook, whatever) did a scan of your inbox, even if only to display the message subject/from/date, then the message is moved away from new and into cur. Don't pay attention to tmp since it is only used temporarily (and very briefly) by the software delivering messages into your maildir.
There may be some files and directories within your ~/Maildir called couriersomething... these are usually handled by the IMAP server and you shouldn't mess with them (at least until you do understand how they are used)... however all (most?) of these files are plain text files that you can look into if you are curious.
b. I see these x-headers in my full headers:
X-DH-Virus-Scanned: Debian amavisd-new at madmax.dreamhost.com
X-Spam-Status: No, score=x tagged_above=-999 required=999 WHITELISTED tests=
The spam x-header might be right, but the virus scan looks like something dreamhost has installed, rather than the clamassassin x-headers suggested by John Paulette's article:
I didn't read the article you refer but dreamhost has its own version of SpamAssassin installed as described in http://wiki.dreamhost.com/Junk_Mail.
You probably have junk mail filtering enabled in your domain (see https://panel.dreamhost.com/index.cgi?tree=mail.junk).
Nope... you can have as many spamassassins working on the same message as you want (can). Only be sure to use different headers in each instance, since you can't modify dreamhost's spamassassin, use a different header name for your installation... I guess you should also read http://wiki.dreamhost.com/SpamAssasin.
I don't think you are able to create folders outside (i.e. at the same level as the inbox), at least not with the webmail provided by dreamhost... I just tried and it didn't let me do so... I also tried to do it via IMAP (with Thunderbird) and, although I didn't get any error message, the folder didn't get created. You can only create folders within other folders (starting with inbox).
As for the autocreation of the Junk/Trash folders... I think that Sent, Trash and Drafts are autocreated the first time you enter webmail (that is, squirrelmail creates them)... I think other imap clients also auto-create some folders (I think Thunderbird only auto-creates Trash).
I think (but I'm not sure) that if you name a non-existant folder in a rule in procmail, the folder is created when (and if) the rule is actually executed (e.g. by a message hitting it). BUT... the folder won't be subscribed to... that is, it won't show in your webmail or imap client folder list... you'll have to manually subscribe to it via you webmail folders settings or the subscribe option in your imap client (the subscription is server based, so subscribing in one of them is enough so that can be seen in every client).
'Junk Mail' is a special case... please read http://wiki.dreamhost.com/Junk_Mail ... it is not a folder that you can see other than by the specially modified webmail client that dreamhost gives you at webmail.[/i]yourdomain.com[/i]. You won't be able to see it as a folder within your ~/Maildir since it actually resides (I think) in dreamhost's anti-spam server farm and you get to sneak it via webmail in order to delete or let pass thru the quarantined messages that dh's anti-spam identified as spam and captured (you have to configure this... keep reading http://wiki.dreamhost.com/Junk_Mail .
Dreamhost doesn't delete your mail until you tell it to... IIRC, the default settings when you create an address within a junk-mail protected domain, it is configured to not block or tag anything. If you want to stop most spam, you may want to configure each mailbox junk settings to block mail at 4 or 5 and to keep quarantined messages for 30 days -the maximum allowed (you do this from the webmail spamassassin configuration options).
Mmmhhh I know very little procmail (though I have it working for my parents and wife, I myself use maildrop)... a quick google on this suggests me (though I really, really can be very wrong about this) that this is not possible to do within procmail... you'd have to pipe your message to a script to do this, but I think that not being done within procmail defeats what you actually want to do... maybe some procmail wizard will be able to help you on this...
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