diff --git a/gnu/tests/mail.scm b/gnu/tests/mail.scm
index f13751b72f..8a2dbd798f 100644
--- a/gnu/tests/mail.scm
+++ b/gnu/tests/mail.scm
@@ -301,8 +301,19 @@ (define %dovecot-os
                      (auth-anonymous-username "alice")
                      (mail-location
                       (string-append "maildir:~/Maildir"
-                                     ":INBOX=~/Maildir/INBOX"
-                                     ":LAYOUT=fs"))))))
+                                     ":LAYOUT=fs"))
+                     (namespaces
+                      (list
+                       (namespace-configuration
+                        (name "INBOX")
+                        (inbox? #t)
+                        (separator "/")
+                        (location "maildir:~/Maildir/INBOX"))
+                       (namespace-configuration
+                        (name "guix-devel")
+                        (separator "/")
+                        (prefix "guix-devel/")
+                        (location "maildir:~/Maildir/guix-devel"))))))))
 
 (define (run-dovecot-test)
   "Return a test of an OS running Dovecot service."
@@ -351,9 +362,10 @@ (define message "From: test@example.com\n\
               (marionette-eval `(file-exists? (string-append "/proc/" ,pid))
                                marionette)))
 
-          (test-assert "accept an email"
+          (define-syntax-rule (with-imap-connection imap exp ...)
             (let ((imap (socket AF_INET SOCK_STREAM 0))
-                  (addr (make-socket-address AF_INET INADDR_LOOPBACK 8143)))
+                  (addr (make-socket-address AF_INET INADDR_LOOPBACK 8143))
+                  (body (lambda (imap) exp ...)))
               (connect imap addr)
               ;; Be greeted.
               (read-line imap) ;OK
@@ -362,6 +374,43 @@ (define message "From: test@example.com\n\
               (read-line imap) ;+
               (write-line "c2lyaGM=" imap)
               (read-line imap) ;OK
+
+              (let ((ok (body imap)))
+                ;; Logout
+                (write-line "a LOGOUT" imap)
+                (close imap)
+                ok)))
+
+          (define (marionette-read-new-mail mailbox marionette)
+            (marionette-eval
+             `(begin
+                (use-modules (ice-9 ftw)
+                             (ice-9 match))
+                (match (scandir ,mailbox)
+                  (("." ".." message-file)
+                   (call-with-input-file
+                       (string-append ,mailbox message-file)
+                     get-string-all))))
+             marionette))
+
+          (test-assert "accept an email"
+            (with-imap-connection imap
+              ;; Append a message to the INBOX mailbox
+              (write-line (format #f "a APPEND INBOX {~a}"
+                                  (number->string (message-length message)))
+                          imap)
+              (read-line imap) ;+
+              (write-line message imap)
+              (read-line imap) ;OK
+              #t))
+
+          (test-equal "mail arrived"
+            message
+            (marionette-read-new-mail "/home/alice/Maildir/INBOX/new/"
+                                      marionette))
+
+          (test-assert "accept an email in fresh mailbox"
+            (with-imap-connection imap
               ;; Create a TESTBOX mailbox
               (write-line "a CREATE TESTBOX" imap)
               (read-line imap) ;OK
@@ -372,24 +421,16 @@ (define message "From: test@example.com\n\
               (read-line imap) ;+
               (write-line message imap)
               (read-line imap) ;OK
-              ;; Logout
-              (write-line "a LOGOUT" imap)
-              (close imap)
               #t))
 
-          (test-equal "mail arrived"
+          (test-equal "mail arrived in fresh mailbox"
             message
-            (marionette-eval
-             '(begin
-                (use-modules (ice-9 ftw)
-                             (ice-9 match))
-                (let ((TESTBOX/new "/home/alice/Maildir/TESTBOX/new/"))
-                  (match (scandir TESTBOX/new)
-                    (("." ".." message-file)
-                     (call-with-input-file
-                         (string-append TESTBOX/new message-file)
-                       get-string-all)))))
-             marionette))
+            (marionette-read-new-mail "/home/alice/Maildir/TESTBOX/new/"
+                                      marionette))
+
+          (test-assert "mailbox exists"
+            (marionette-eval `(file-exists? "/home/alice/Maildir/guix-devel")
+                             marionette))
 
           (test-end))))