diff --git a/modoboa/lib/smtp_backend.py b/modoboa/lib/smtp_backend.py
index 88a86776d..234ff12d4 100644
--- a/modoboa/lib/smtp_backend.py
+++ b/modoboa/lib/smtp_backend.py
@@ -36,6 +36,7 @@ class OAuthBearerEmailBackend(EmailBackend):
                 self.connection.starttls(context=self.ssl_context)
             if self.username and self.password:
                 token = oauth2.build_oauthbearer_string(self.username, self.password)
+                self.connection.ehlo(DNS_NAME.get_fqdn())
                 self.connection.docmd("AUTH", f"OAUTHBEARER {token.decode('utf-8')}")
             return True
         except OSError: