diff --git a/CHANGELOG.md b/CHANGELOG.md
index 559a2d5d..49fc78fb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 * Improvement: catch lack of support of PERIOD in vobject <= 0.9.9
 * Fix: sharing: backmap of REPORT/PROPPATCH hrefs is now URL-encode-aware (edit of a shared collection failed when the principal contains '@')
 * Workaround: remove trailing spaces on TZID and TZNAME appended by buggy Microsoft clients
+* Extension: [auth] imap_append_domain option (optional)
 
 ## 3.7.5
 * Add: [sharing] conversion_bday_summary_template (customize summary)
diff --git a/DOCUMENTATION.md b/DOCUMENTATION.md
index c76f70e2..7bfa9e72 100644
--- a/DOCUMENTATION.md
+++ b/DOCUMENTATION.md
@@ -1389,6 +1389,14 @@ One of:
 
 Default: `tls`
 
+##### imap_append_domain
+
+_(>= 3.7.6)_
+
+Append `@` + domain to login before trying IMAP connection
+
+Default: (unset)
+
 ##### oauth2_token_endpoint
 
 _(>= 3.5.0)_
diff --git a/config b/config
index 904986a6..2bd39383 100644
--- a/config
+++ b/config
@@ -161,6 +161,10 @@
 # Value: tls | starttls | none
 #imap_security = tls
 
+# Append '@' + domain to login before trying IMAP connection (optional)
+# Value: domain.tld
+#imap_append_domain =
+
 # OAuth2 token endpoint URL
 #oauth2_token_endpoint = <URL>
 
diff --git a/radicale/auth/imap.py b/radicale/auth/imap.py
index f0d52b47..e9a1dfd4 100644
--- a/radicale/auth/imap.py
+++ b/radicale/auth/imap.py
@@ -48,6 +48,11 @@ class Auth(auth.BaseAuth):
                 logger.info("auth imap port (autoselected): %d", self._port)
             else:
                 logger.info("auth imap port: %d", self._port)
+        self._append_domain = self.configuration.get("auth", "imap_append_domain")
+        if self._append_domain is None or len(self._append_domain) == 0:
+            logger.info("auth imap append domain not used")
+        else:
+            logger.info("auth imap append domain: %s", self._append_domain)
 
     def _login(self, login, password) -> str:
         try:
@@ -63,21 +68,25 @@ class Auth(auth.BaseAuth):
                 connection = imaplib.IMAP4(host=self._host, port=self._port)
                 if self._security == "starttls":
                     connection.starttls(ssl.create_default_context())
+            if self._append_domain is None or len(self._append_domain) == 0:
+                imaplogin = login
+            else:
+                imaplogin = login + "@" + self._append_domain
             try:
                 if "AUTH=PLAIN" in connection.capabilities:
-                    logger.debug("IMAP authentication PLAIN selected for user %r via %s:%d (security: %s)", login, self._host, self._port, self._security)
+                    logger.debug("IMAP authentication PLAIN selected for user %r via %s:%d (security: %s)", imaplogin, self._host, self._port, self._security)
                     connection.authenticate(
                         "PLAIN",
-                        lambda _: "{0}\x00{0}\x00{1}".format(login, password).encode(),
+                        lambda _: "{0}\x00{0}\x00{1}".format(imaplogin, password).encode(),
                     )
                 elif "AUTH=LOGIN" in connection.capabilities:
-                    logger.debug("IMAP authentication LOGIN selected for user %r via %s:%d (security: %s)", login, self._host, self._port, self._security)
-                    connection.login(login, password)
+                    logger.debug("IMAP authentication LOGIN selected for user %r via %s:%d (security: %s)", imaplogin, self._host, self._port, self._security)
+                    connection.login(imaplogin, password)
                 else:
                     logger.error("IMAP server is neither supporting AUTH=PLAIN or AUTH=LOGIN: %s:%d (security: %s)", self._host, self._port, self._security)
                     return ""
             except imaplib.IMAP4.error as e:
-                logger.warning("IMAP authentication failed for user %r: %s", login, e, exc_info=False)
+                logger.warning("IMAP authentication failed for user %r: %s", imaplogin, e, exc_info=False)
                 return ""
             connection.logout()
             return login
diff --git a/radicale/config.py b/radicale/config.py
index cf390a2d..9554e4ff 100644
--- a/radicale/config.py
+++ b/radicale/config.py
@@ -440,6 +440,10 @@ DEFAULT_CONFIG_SCHEMA: types.CONFIG_SCHEMA = OrderedDict([
             "value": "tls",
             "help": "Secure the IMAP connection: *tls*|starttls|none",
             "type": imap_security}),
+        ("imap_append_domain", {
+            "value": "",
+            "help": "Append '@' + domain to login before trying IMAP connection",
+            "type": str}),
         ("oauth2_token_endpoint", {
             "value": "",
             "help": "OAuth2 token endpoint URL",