I second that! This saved the day for me. Thanks to Sönke for the answer and Louie for starting the thread.

On Tue, 10 Nov 2015 08:50:03 GMT, Louie Bacani Foronda wrote:

On Sat, 7 Nov 2015 21:15:06 +0100, Sönke Ludwig wrote:

Am 07.11.2015 um 19:40 schrieb Louie Bacani Foronda:

How to fix this, is there a way to not verify the certificate?

Connecting TLS tunnel: error:14090086:SSL routines:SSL3GETSERVER_CERTIFICATE:certificate verify failed (336134278)

You can modify the TSLContext like this: 

auto settings = new SMTPClientSettings;
// ...
settings.tlsContextSetup = (scope ctx) {
	ctx.peerValidationMode = TLSPeerValidationMode.none;
};

sendMail(settings, ...);

Instead of TLSPeerValidationMode.checkPeer might also work and is a
little safer. Alternatively, ctx.useTrustedCertificateFile(...) can be
used to register the appropriate root authority.

You are a lifesaver! I used the useTrustedCertificateFile(); I found mine on /etc/ssl/certs/ca-certificate.crt

awesome!