diff --git a/roles/mail_server/templates/99-local.conf.j2 b/roles/mail_server/templates/99-local.conf.j2
index 077a7b59ee6dda1c63f4adb8cae4b57c08019ad6..6b34cb7e620c84c450a4ff602c91a376d2f2c888 100644
--- a/roles/mail_server/templates/99-local.conf.j2
+++ b/roles/mail_server/templates/99-local.conf.j2
@@ -31,6 +31,7 @@ service auth {
 # TLS configuration.
 ssl_cert = </etc/ssl/certs/{{ ansible_fqdn }}_imap.pem
 ssl_key = </etc/ssl/private/{{ ansible_fqdn }}_imap.key
+ssl_dh_parameters_length = 2048
 ssl_protocols = {{ mail_server_tls_protocols | join(' ') }}
 ssl_cipher_list = {{ mail_server_tls_ciphers }}
 ssl = required