When IMSS for Windows self-signed Transport Layer Security (TLS) certificate expired, IMSS may fail to deliver incoming emails using the certificate with its TLS settings. This can also affect clients who did an in-place upgrade of IMSS 7.0 to version 7.1, or IMSS 7.1 to IMSS 7.5.
To resolve this issue:
- Generate a new self-signed certificate.
- Run the following command to change the certificate format to PFX:
openssl pkcs12 -export -out text.pfx -in certificate.pem
where "certificate.pem" is the .PEM file generated in Step 1.