diff --git a/debian/README.Debian b/debian/README.Debian
index d32a3f0e06..aefa76aae1 100644
--- a/debian/README.Debian
+++ b/debian/README.Debian
@@ -46,6 +46,9 @@ required, you can copy ssl certificate and key to /etc/gitlab/ssl as gitlab.crt
 and gitlab.key. If letsencrypt option is selected, symbolic links are added for
 certificates obtained using letsencrypt to /etc/gitlab/ssl.
 
+9. exim compatibility issue: If you use exim as your mta, then see
+https://github.com/gitlabhq/gitlabhq/issues/4866#issuecomment-145784636
+
 Useful diagnostics
 ==================