Symptoms
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When connecting to a mail server over SSL via an email client (e.g. Outlook), connection fails:
PLESK_INFO: Your server does not support the connection encryption type you have specified. Try changing the encryption method.
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One of the following error messages appears in the
/var/log/mailloglogfile:postfix/smtpd[25460]: warning: TLS library problem: error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol:s23_srvr.c:640:
dovecot: pop3-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=203.0.113.2, lip=203.0.113.3, TLS handshaking: SSL_accept() failed: error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol
Cause
TLSv1, SSLv3 or SSLv2 protocol support, which is required for old email clients/old software (e.g, WinHTTP-based applications on Windows 7) is disabled in Postfix/Dovecot configuration.
By default, SSL protocols SSLv2 and SSLv3 are disabled in Postfix/Dovecot configuration as these protocols are vulnerable to the POODLE attack.
Resolution
The best practice is to use the latest available version of email clients that support connections over TLS 1.1 and 1.2.
For WinHTTP-based applications, refer to the Microsoft article.
If for some reason it is not possible, apply the following steps:
Note: This guide is intended for Plesk administrators. If you are a domain owner, please contact your service provider for assistance with email account configuration.
Enable the TLSv1 protocol in Postfix configuration
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Connect to the Plesk server via SSH.
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Enable support for TLSv1 protocol:
# plesk sbin pci_compliance_resolver –disable postfix
To find out whether TLSv1 version is enabled in Postfix or not, run the command:
# egrep “smtpd_tls_mandatory_protocols|smtpd_tls_protocols” /etc/postfix/main.cf
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Restart Postfix:
# service postfix restart
Enable the TLSv1 protocol in Dovecot configuration
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Connect to the Plesk server via SSH.
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Open the file
/etc/dovecot/conf.d/11-plesk-security-ssl.confin a text editor (for example, vi editor) and change the values ofssl_min_protocolandssl_protocolsas follows:ssl_protocols = TLSv1 TLSv1.1 TLSv1.2
ssl_min_protocol=TLSv1To find out whether TLSv1 version is enabled in Dovecot or not, run the command:
# egrep “ssl_protocols|ssl_min_protocol” /etc/dovecot/conf.d/11-plesk-security-ssl.conf
Note: If TLSv1 is not enabled it will not be shown in the output.
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Restart Dovecot service:
# service dovecot restart
Enable the TLSv1 protocol in Courier configuration
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Connect to the Plesk server via SSH.
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Open the files
/etc/courier-imap/pop3d-ssand/etc/courier-imap/imapd-sslin a text editor (for example, vi editor) and change the values ofTLS_PROTOCOLandTLS_STARTTLS_PROTOCOLas follows:# grep PROTOCOL /etc/courier-imap/pop3d-ssl | grep -v ^#
TLS_PROTOCOL=TLSv1+
TLS_STARTTLS_PROTOCOL=TLSv1+# grep PROTOCOL /etc/courier-imap/imapd-ssl | grep -v ^#
TLS_PROTOCOL=TLSv1+
TLS_STARTTLS_PROTOCOL=TLSv1+ -
Restart Courier services:
# service courier-imaps restart
# service courier-pop3s restart
# service courier-imapd restart
# service courier-pop3d restart
# service xinetd restart
If an email client still does not allow to connect, enable the SSLv2 and SSLv3 protocols in Postfix configuration:
Warning: Such configuration is not recommended due to security vulnerabilities. Apply it at your own risk…
