Unable to send message from Roundcube: SMTP Error (-1): Connection to server failed

Symptoms

• The following error pops up after logging into Roundcube WebMail:

  CONFIG_TEXT: Connection to storage server failed

• Unable to send a message using Roundcube webmail with the following error:

  PLESK_INFO: SMTP Error (-1): Connection to server failed

• The entries like below can be found in /var/log/maillog:

  CONFIG_TEXT: admin dovecot: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=::1, lip=::1, TLS handshaking: SSL_accept() failed: error:14094415:SSL routines:SSL3_READ_BYTES:sslv3 alert certificate expired: SSL alert number 45, session=

  OR

  CONFIG_TEXT:  Jun 24 23:12:38 hostname postfix/smtpd[2273742]: warning: TLS library problem: error:14094415:SSL routines:SSL3_READ_BYTES:sslv3 alert certificate expired:s3_pkt.c:1275:SSL alert number 45:

• The error below is found in the /var/log/plesk-roundcube/errors:

  CONFIG_TEXT: ERROR: stream_socket_client(): unable to connect to ssl://localhost:465 (Unknown error) (0)
  ERROR: Failed to connect socket: stream_socket_client(): unable to connect to ssl://localhost:465 (Unknown error) ()
  <fav2islm> SMTP Error: Connection failed: Failed to connect socket: stream_socket_client(): unable to connect to ssl://localhost:465 (Unknown error) in /usr/share/psa-roundcube/program/lib/Roundcube/rcube.php on line 1667 (POST /?_task=mail&_unlock=loading1533740030256&_lang=es&_framed=1&_action=send)

• While checking the certificate on mail server (replace example.com with the valid domain name or hostname), it can be seen that certificate expired:

  # echo | openssl s_client -connect example.com:465 -servername example.com 2>/dev/null | grep 'Verify return code'
  Verify return code: 10 (certificate has expired)

Cause

Mail server SSL/TLS certificate expired.

Resolution

It is required to renew the certificate for Mail Server.

For that, log into Plesk and update the mail server's certificate.

Additional information

Unable to log into RoundCube webmail in Plesk: Connection to storage server failed

Unable to log into RoundCube: Connection to storage server failed