[FIXED BUG] Unable to remove old default certificate after setting a new default certificate: Unable to remove SSL/TLS certificates. One of the certificates you are going to delete is used for securing the mail server

Symptoms

Unable to remove old default certificate after creating a new default certificate in Tools & Settings > SSL certificates:

PLESK_ERROR: Unable to remove SSL/TLS certificates.
One of the certificates you are going to delete is used for securing the mail server.
Plesk was installed with the following option --install-component msmtp via CLI.
Eventhough Plesk was intalled without a Mailserver the default certificate is assigned to the Mailserver in database:

# plesk db "select * from ServiceNodeConfiguration where serviceNodeId=1 and section='mailServer' and name='inbound_ssl'"
-----------------------------------------+
serviceNodeId section name value
-----------------------------------------+
1 mailServer inbound_ssl true
-----------------------------------------+
1 row in set (0.00 sec)

# plesk db "select * from ServiceNodeConfiguration where serviceNodeId=1 and section='mailServer' and name='inbound_ssl_cert_id'"
-------------------------------------------------+
serviceNodeId section name value
-------------------------------------------------+
1 mailServer inbound_ssl_cert_id 2

Product issue:

#PPP-44652 "If Plesk was installed without the mail server (MSMTP), the default SSL/TLS certificate can now be removed."
Fixed in:
- Plesk Obsidian 22 October 2019 (Linux)

Please consider updating your server:

If update is not possible for some reason you may try the following

workaround

Connect to the server via SSH.
Access Plesk database with plesk db:
Remove old default certificate from database:

MYSQL_LIN: delete from ServiceNodeConfiguration where serviceNodeId=1 and section='mailServer' and name='inbound_ssl';

MYSQL_LIN: delete from ServiceNodeConfiguration where serviceNodeId=1 and section='mailServer' and name='inbound_ssl_cert_id';