Yes, but no.
The solution proposed by DH is the following:
You set up the filters via the control panel to catch all incoming mail. I've modified them as follows:
i) First, add the header X-MyEmail-Unfiltered: 1 to emails without X-MyEmail-Unfiltered: 1 in the headers and then continue.
ii) Then, move emails with X-MyEmail-Dest: Inbox in the headers to Inbox and then stop.
iii) Then, forward emails that Do not contain X-MyEmail-Dest: in the headers to [SHELL USER]
iv) Finally, move emails with X-MyEmail-Unfiltered: 1 in the headers to Inbox and then stop.
In this situation, [SHELL USER] is a user that you have that still has shell access (Like the one that had a Maildir).
Ok, so the messages come in and since all of them are tagged with the X-MyEmail-Unfiltered: 1 header in the first filter, they are forwarded to the shell user. You then do your filtering using procmail, spam assassin, etc but WITHOUT A MAILDIR and then (at the end), you forward those messages back to your e-mail address (this time with X-MyEmail-Unfiltered set to false and with X-MyEmail-Dest: Inbox) and the messages will be deposited in your inbox of the MAIL user (i.e. not the shell user).
The key conceptual thing to understand is that you may have a mail user and a shell user that share the user name. Huh??? that is, you may have firstname.lastname@example.org to receive mail. That user is on the mail server and can and will receive mail. But, then you also have email@example.com as a SHELL USER which can also receive mail forwarded from the MAIL USER, but cannot deliver that mail to any maildir but can forward that mail back to firstname.lastname@example.org (MAIL USER).
So, that's the solution proposed by DH.
Obviously, the moment that you start forwarding mail to the shell user and back, you start the counter counting for your sender quota and you stand a very good chance of getting blocked. That is where I am at. DH says that they can ask the abuse department to give me a larger quota, but they absolutely refuse to allow me to go back to being able to use procmail with a Maildir. And, they don't have any solution to keep me from exceeding the sender quota for what is (for all intents and purposes) internal traffic on their internal network to shuttle messages from one DH server to another.
I have to say that I'm not looking forward to modifying all my filters that I had made and I don't trust DH to not block my incoming mail causing it to be returned to sender as undeliverable.
It's encouraging me to look for another provider.