diff --git a/client_software/0020_nextcloud_mozilla_pre/user_run.sh b/client_software/0020_nextcloud_mozilla_pre/user_run.sh
index b266be2..d561817 100755
--- a/client_software/0020_nextcloud_mozilla_pre/user_run.sh
+++ b/client_software/0020_nextcloud_mozilla_pre/user_run.sh
@@ -4,6 +4,7 @@
 #
 # Will prepare local mozilla and thunderbird folders with given tar.files
 #
+import re
 import sys
 import subprocess
 import certifi
@@ -106,4 +107,85 @@ if 'PROFILE_TB_SRC' in environ: # Check and setup mozilla
     print("Done.")
     #Next sync will be executed by logon script
 
+# Check and auto-provision IMAP account for DAVTOKEN_USER@TLDOMAIN in Thunderbird
+if ('PROFILE_TB_DST' in environ and 'TLDOMAIN' in environ and
+        'SERVERFQDN_IMAP' in environ and 'DAVTOKEN_USER' in environ):
+  prefs_path = environ['PROFILE_TB_DST'] + "/default/prefs.js"
+  mail_user = environ['DAVTOKEN_USER'] + "@" + environ['TLDOMAIN']
+  mail_user_url = mail_user.replace('@', '%40')
+  imap_host = environ['SERVERFQDN_IMAP']
+  full_name = environ.get('TB_MAIL_FULLNAME', environ['DAVTOKEN_USER'])
+  profile_dir = environ['PROFILE_TB_DST'] + "/default"
+
+  if not os.path.exists(prefs_path):
+    print("Thunderbird prefs.js not found, skipping mail account setup.")
+  else:
+    with open(prefs_path, 'r') as f:
+      prefs = f.read()
+
+    account_exists = bool(re.search(
+      r'mail\.server\.server\d+\.userName",\s*"' + re.escape(mail_user) + '"',
+      prefs
+    ))
+    if account_exists:
+      print(f"Thunderbird IMAP account for {mail_user} already configured.")
+    else:
+      print(f"Adding Thunderbird IMAP account for {mail_user} ...")
+
+      server_nums  = [int(x) for x in re.findall(r'mail\.server\.server(\d+)\.type', prefs)]
+      account_nums = [int(x) for x in re.findall(r'mail\.account\.account(\d+)\.server', prefs)]
+      id_nums      = [int(x) for x in re.findall(r'mail\.identity\.id(\d+)\.useremail', prefs)]
+
+      ns = (max(server_nums)  + 1) if server_nums  else 1
+      na = (max(account_nums) + 1) if account_nums else 1
+      ni = (max(id_nums)      + 1) if id_nums      else 1
+      sn, an, idn = f"server{ns}", f"account{na}", f"id{ni}"
+
+      new_lines = [
+        f'user_pref("mail.server.{sn}.check_new_mail", true);',
+        f'user_pref("mail.server.{sn}.cleanup_inbox_on_exit", true);',
+        f'user_pref("mail.server.{sn}.directory", "{profile_dir}/ImapMail/{imap_host}");',
+        f'user_pref("mail.server.{sn}.directory-rel", "[ProfD]ImapMail/{imap_host}");',
+        f'user_pref("mail.server.{sn}.hostname", "{imap_host}");',
+        f'user_pref("mail.server.{sn}.login_at_startup", true);',
+        f'user_pref("mail.server.{sn}.max_cached_connections", 5);',
+        f'user_pref("mail.server.{sn}.name", "{mail_user}");',
+        f'user_pref("mail.server.{sn}.port", 993);',
+        f'user_pref("mail.server.{sn}.socketType", 3);',
+        f'user_pref("mail.server.{sn}.storeContractID", "@mozilla.org/msgstore/maildirstore;1");',
+        f'user_pref("mail.server.{sn}.timeout", 29);',
+        f'user_pref("mail.server.{sn}.trash_folder_name", "Trash");',
+        f'user_pref("mail.server.{sn}.type", "imap");',
+        f'user_pref("mail.server.{sn}.userName", "{mail_user}");',
+        f'user_pref("mail.identity.{idn}.draft_folder", "imap://{mail_user_url}@{imap_host}/Drafts");',
+        f'user_pref("mail.identity.{idn}.drafts_folder_picker_mode", "0");',
+        f'user_pref("mail.identity.{idn}.fcc_folder", "imap://{mail_user_url}@{imap_host}/Sent");',
+        f'user_pref("mail.identity.{idn}.fcc_folder_picker_mode", "0");',
+        f'user_pref("mail.identity.{idn}.fullName", "{full_name}");',
+        f'user_pref("mail.identity.{idn}.reply_on_top", 1);',
+        f'user_pref("mail.identity.{idn}.stationery_folder", "imap://{mail_user_url}@{imap_host}/Templates");',
+        f'user_pref("mail.identity.{idn}.tmpl_folder_picker_mode", "0");',
+        f'user_pref("mail.identity.{idn}.useremail", "{mail_user}");',
+        f'user_pref("mail.identity.{idn}.valid", true);',
+        f'user_pref("mail.account.{an}.identities", "{idn}");',
+        f'user_pref("mail.account.{an}.server", "{sn}");',
+      ]
+
+      # Append account to mail.accountmanager.accounts
+      m = re.search(r'(mail\.accountmanager\.accounts",\s*")([^"]+)(")', prefs)
+      if m:
+        prefs = prefs[:m.start(2)] + m.group(2) + ',' + an + prefs[m.end(2):]
+      else:
+        new_lines.append(f'user_pref("mail.accountmanager.accounts", "{an}");')
+
+      # Update mail.account.lastKey
+      m = re.search(r'(mail\.account\.lastKey",\s*)(\d+)', prefs)
+      if m:
+        prefs = prefs[:m.start(2)] + str(max(int(m.group(2)), na)) + prefs[m.end(2):]
+
+      prefs = prefs.rstrip('\n') + '\n' + '\n'.join(new_lines) + '\n'
+      with open(prefs_path, 'w') as f:
+        f.write(prefs)
+      print(f"Thunderbird IMAP account for {mail_user} added successfully.")
+
 sys.exit(0)
diff --git a/config/setup_system.conf.dist b/config/setup_system.conf.dist
index 8c04d4a..df0653f 100644
--- a/config/setup_system.conf.dist
+++ b/config/setup_system.conf.dist
@@ -77,6 +77,10 @@ if [ "$EUID" -ne 0 ]; then
   #Thunderbird Profiles
   export PROFILE_TB_SRC="mozilla_profiles/thunderbird"
   export PROFILE_TB_DST="${DECRYPTEDDATADIR}/thunderbird"
+
+  # Mail account auto-provisioning for DAVTOKEN_USER@TLDOMAIN in Thunderbird
+  export SERVERFQDN_IMAP="imap.${TLDOMAIN}"  # IMAP server hostname (e.g. imap.strato.de)
+  export TB_MAIL_FULLNAME="${USER}"           # Display name written to the Thunderbird identity
 fi
 
 #Basic commons not needing change