If the e-mail certificates are stored on an e-mail gateway (a server-side encryption solution), the certificate should be left in place.
Alternatively, you can also archive the certificate.
This makes it possible to read old encrypted e-mails of the departing employee in plain text.
An even better option is to deactivate the e-mail account of the employee concerned in order to prevent further use by the employee.
In principle, it is recommended that important e-mails are stored decrypted in a separate protected place in order to avoid inconvenience if the private key is lost or the e-mail certificate is accidentally deleted.
If you have any further questions, please do not hesitate to contact our support team on +49 661 480 276 10.