Question

I have been using Email::Sender with Email::Sender::Transport::SMTP::TLS send email using a STARTTLS enabled relay. The relay has recently changed to using X.509 certificates for authentication. However I note that Email::Sender::Transport::SMTP::TLS has no option to point to my certificate. Neither does Net::SMTP::TLS on which Email::Sender::Transport::SMTP::TLS is based.

Can someone suggest a solution? Another module perhaps that will allow me to authenticate using a certificate.

Thank you

Answer 1

Checking the dependency tree: Email::Sender::Transport::SMTP::TLS ==> Net::SMTP::TLS::ButMaintained ==> IO::Socket::SSL ==> Net::SSLeay

Both IO::Socket::SSL and Net::SSLeay supporting the X.509 client certificates. So Net::SMTP::TLS::ButMaintained and Email::Sender::Transport::SMTP::TLS should be enhanced to support client certificates. A proper way should update both modules to allow the SSL_key|SSL_key_file and SSL_cert|SSL_cert_file parameters.

Here is a quick dirty one — you need to create modified Net::SMTP::TLS::ButMaintained and keep it locally.

# modify the Net::SMTP::TLS::ButMaintained; 
# built a private version which have client certificates
sub starttls {
    my $me = shift;
    $me->_command("STARTTLS");
    my ( $num, $txt ) = $me->_response();
    if ( not $num == 220 ) {
        croak "Invalid response for STARTTLS: $num $txt\n";
    }
    if (
        not IO::Socket::SSL::socket_to_SSL(
            $me->{sock}, 
            SSL_version => "SSLv3 TLSv1", 
            ### private changes begin: append following two lines. 
            SSL_use_cert => 1,
            SSL_cert_file => "path_to/your/certificate_file.pem",
            SSL_key_file => "path_to/your/private_key_file.pem"
            ### private changes end:
        )
      )
    {
        croak "Couldn't start TLS: " . IO::Socket::SSL::errstr . "\n";
    }
    $me->hello();
}

Please leave the User and Password parameter as blank.

Good luck!