Mail from specific servers gets rejected at Plesk Panel server. In mail client following message appears:
An error occurred sending mail: Unable to establish a secure link with SMTP server mail.solarnex.com using STARTTLS since it doesn't advertise that feature. Switch off STARTTLS for that server or contact your service provider.
/usr/local/psa/var/log/maillog file there are following messages:
localhost postfix/smtpd: NOQUEUE: reject: RCPT from mail.server: 554 5.7.1 Service unavailable; Client host [184.108.40.206] blocked using zen.dnsbl; http://www.spamhaus.org/query/bl?ip=220.127.116.11; from=<email@example.com> to=<firstname.lastname@example.org> proto=ESMTP helo=<mail.server> localhost /usr/lib64/plesk-9.0/psa-pc-remote: Message aborted.
The IP-address of sending server is listed in spam block lists.
Either delete blocking spam list server from Plesk Panel at Tools & Settings > Mail Server Settings > Switch on spam protection based on DNS blackhole lists > DNS zones for DNSBL service or check more information in the URL provided at
maillog. In current case it is http://www.spamhaus.org/lookup/.