diff -up dovecot-2.3.15/doc/dovecot-openssl.cnf.bigkey dovecot-2.3.15/doc/dovecot-openssl.cnf
--- dovecot-2.3.15/doc/dovecot-openssl.cnf.bigkey	2021-06-21 20:24:51.913456628 +0200
+++ dovecot-2.3.15/doc/dovecot-openssl.cnf	2021-06-21 20:25:36.352912123 +0200
@@ -1,5 +1,5 @@
 [ req ]
-default_bits = 2048
+default_bits = 3072
 encrypt_key = yes
 distinguished_name = req_dn
 x509_extensions = cert_type