Initial impl of import from mailbox user task

modules/joex/src/main/resources/reference.conf

@@ -90,6 +90,28 @@ docspell.joex {
     wakeup-period = "10 minutes"
   }
 
+  # Configuration for the user-tasks.
+  user-tasks {
+    # Allows to import e-mails by scanning a mailbox.
+    scan-mailbox {
+      # A limit of how many folders to scan through. If a user
+      # configures more than this, only upto this limit folders are
+      # scanned and a warning is logged.
+      max-folders = 50
+
+      # How many mails (headers only) to retrieve in one chunk.
+      mail-chunk-size = 100
+
+      # A limit on how many mails to process in one job run. This is
+      # only to avoid resource allocation to one user/collective.
+      #
+      # If more than this number of mails is encountered, a warning is
+      # logged.
+      max-mails = 1000
+    }
+  }
+
+
   # Docspell uses periodic house keeping tasks, like cleaning expired
   # invites, that can be configured here.
   house-keeping {