Which version  of Merucry? If not V4.8 you should update to have OpenSSL.

[quote]Now I get the message

2018-04-29 08:55:05 Connection failed. Error #2:

stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL

Error messages:error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert

handshake failure

[D:\testl\PHPMailer\src\SMTP.php line

404]

SMTP Error: Could not connect to SMTP host.[/quote]

 If this is with Mercury 4.8, You should check the settings of Module SmtpS. Usualy StartTLS is port 537 while SSL is port 465. Perhaps because of error on deprecated SSL V3 you have to enable "Support for deprecated  direct-connect SSL".And you have to insert or create an certificate file

Hallo,

when I try to send a mail, I get the message

SMTP INBOUND: "502 STARTTLS not enabled by administrator."
Where/how can I enable STARTTLS?

To enable SSL support for SMTP in Mercury go to Configuration / MercuryS SMTP Server / SSL.

Thanks,

I've had a lttle progress.

Now I get the message

2018-04-29 08:55:05 Connection failed. Error #2:

stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL

Error messages:error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert

handshake failure

[D:\testl\PHPMailer\src\SMTP.php line

404]

SMTP Error: Could not connect to SMTP host.

SMTP.php looks like this:

399        // Begin encrypted connection
400        set_error_handler([$this, 'errorHandler']);
401        $crypto_ok = stream_socket_enable_crypto(
402            $this->smtp_conn,
403            true,
404            $crypto_method
405        );
406        restore_error_handler();

 

We probably can't help much with the php client side, but if you check the MercuryS log file there could be some helpful information there.