I'm trying to send Drupal 8 emails using Swift Mailer (5.4.8, 8.x-1.0-beta1) and a remote SMTP server. The transport should be encrypted, so TLS should be used. This is my setting:
Unfortunatly when trying to send an email I'm getting a warning:
Warning: no valid certs found cafile stream: `/etc/apache2/ssl/certs/' in Swift_Transport_StreamBuffer->startTLS() [...]
And this error afterwards:
Unable to connect with TLS encryption
Without the encryption I'm able to send mails using the remote STMP server.
A test of the connection using TLS from the server where Drupal is installed looks fine (I guess):
openssl s_client -connect mail.example.com:25 -starttls smtp
The response (excerpt):
CONNECTED(00000003) [...] --- No client certificate CA names sent --- SSL handshake has read 4369 bytes and written 586 bytes [...]
So where do I get further details about the connection error? And what could be the cause of the problem?