I can connect and I can send mail to dovecot using LMTP without presenting a certificate: $ ncat pmx1.venev.name INSERT_LMTP_PORT_HERE --ssl 220 pmx1.venev.name Dovecot ready. MAIL FROM: 250 2.1.0 OK RCPT TO: 250 2.1.5 OK DATA 354 OK Subject: This message skipped the MTA and went straight to the MDA . 250 2.0.0 kKAKEm/fXmCbwwAAdB6GMg Saved On Sat, 2021-03-27 at 00:17 +0100, Sebastian wrote:

What I have understand, you are able in configuration to reject transactions with those that doesn't present a valid certificate. Ergo, they can connect, but they can't do anything.

-----Ursprungligt meddelande----- Från: dovecot-bounces@dovecot.org  För Hristo Venev Skickat: den 27 mars 2021 00:16 Till: dovecot@dovecot.org Ämne: ssl_verify_client_cert=yes does not require a client certificate [invalid signature!]

Hello,

I am trying to set up LMTP over TLS. I have set ssl_verify_client_cert:

protocol lmtp {           ssl_ca =

However, clients can still connect without presenting a valid certificate.

In openssl_iostream_set() the flags given to SSL_set_verify() are SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE. For a certificate to be required, the SSL_VERIFY_FAIL_IF_NO_PEER_CERT flag also needs to be set:

diff --git a/src/lib-ssl-iostream/iostream-openssl.c b/src/lib-ssl- iostream/iostream-openssl.c index 5d11526f1..d8df96398 100644 --- a/src/lib-ssl-iostream/iostream-openssl.c +++ b/src/lib-ssl-iostream/iostream-openssl.c @@ -235,7 +235,7 @@ openssl_iostream_set(struct ssl_iostream *ssl_io,                 if (ssl_io->ctx->client_ctx)                         verify_flags = SSL_VERIFY_NONE;                 else -                       verify_flags = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE; +                       verify_flags = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE | +SSL_VERIFY_FAIL_IF_NO_PEER_CERT;                 SSL_set_verify(ssl_io->ssl, verify_flags,                                openssl_iostream_verify_client_cert);         }