Question
How to verify that SSL for IMAP/POP3/SMTP works and a proper certificate is installed?
Answer
Using online checkers
Check SSL using online tools:
Using a Linux server
Any Linux server can be used for these tests. If you do not have a Linux server, use the online checkers above.
To verify SSL, connect to any Linux server via SSH and use the instructions below:
IMAP via SSL using port 993:
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connect to a mail server using
openssl:# openssl s_client -showcerts -connect mail.example.com:993 -servername mail.example.com
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Check output and make sure that a valid certificate is shown:
Server certificate
subject=/OU=Domain Control Validated/OU=PositiveSSL/CN=mail.example.com
issuer=/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 -
Make sure that you received IMAP server response:
* OK [CAPABILITY IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA AUTH=CRAM-MD5 AUTH=PLAIN IDLE ACL ACL2=UNION] Courier-IMAP ready. Copyright 1998-2004 Double Precision, Inc. See COPYING for distribution information.
POP3 via SSL using port 995:
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Connect to a mail server using
openssl:# openssl s_client -showcerts -connect mail.example.com:995 -servername mail.example.com
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Check output and make sure that a valid certificate is shown:
Server certificate
subject=/OU=Domain Control Validated/OU=PositiveSSL/CN=mail.example.com
issuer=/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 -
Make sure that you received POP3 server response:
+OK Hello there. [email protected]
SMTP via SSL using port 465:
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Connect to a mail server using
openssl:# openssl s_client -showcerts -connect mail.example.com:465 -servername mail.example.com
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Check output and make sure that a valid certificate is shown:
Server certificate
subject=/OU=Domain Control Validated/OU=PositiveSSL/CN=mail.example.com
issuer=/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 -
Make sure that you received SMTP server response:
220 mail.example.com ESMTP Postfix
SMTP via TLS/StartTLS using port 25 or 587
Note: To use port 587 the submission port should be enabled in Plesk:
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Connect to a mail server using
openssl:# openssl s_client -starttls smtp -showcerts -connect mail.example.com:25 -servername mail.example.com
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Check output and make sure that a valid certificate is shown:
Server certificate
subject=/OU=Domain Control Validated/OU=PositiveSSL/CN=mail.example.com
issuer=/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 -
Make sure that you received SMTP server response:
250 DSN
with