Checking SSL Certifcate on Plesk Mail Server

Run this command (mail.DOMAIN.de is the MX-Record):

SMTP:
openssl s_client -starttls smtp -crlf -connect mail.DOMAIN.de:25

POP3:
openssl s_client -starttls pop3 -crlf -connect mail.DOMAIN.de:110

IMAP:
openssl s_client -starttls imap -crlf -connect mail.DOMAIN.de:143


As result you can see your certificate if it installed correctly:

Certificate chain

0 s:/description=FmJdZEx3lsXPoIXv/C=DE/CN=mail.DOMAIN.de/emailAddress=hostmaster@DOMAIN.de

   i:/C=IL/O=StartCom Ltd./OU=Secure Digital Certificate Signing/CN=StartCom Class 1 Primary Intermediate Server CA

1 s:/C=IL/O=StartCom Ltd./OU=Secure Digital Certificate Signing/CN=StartCom Class 1 Primary Intermediate Server CA

   i:/C=IL/O=StartCom Ltd./OU=Secure Digital Certificate Signing/CN=StartCom Certification Authority

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How to downgrade Openssl on CentOS?

List the available versions by running this command:

yum --showduplicates list openssl


you should see these lines:

Installed package:
openssl.x86_641:1.0.1e42.el7.9

Available packages:
openssl.x86_64 - 1:1.0.1e-42.el7 - base
openssl.x86_64 - 1:1.0.1e-42.el7_1.5 - updates
openssl.x86_64 - 1:1.0.1e-42.el7.4 - updates
openssl.x86_64 - 1:1.0.1e-42.el7.6 - updates
openssl.x86_64 - 1:1.0.1e-42.el7.8 - updates
openssl.x86_64 - 1:1.0.1e-42.el7.9 - updates

then doing:

yum downgrade openssl-1.0.1e-42.el7_1.5

it will downgrade openssl to 7_1.5 version.