In order to import a huge amount of private certificates at once, all certificates and corresponding keys need to be available in pem format and all together copied in a single file.
Then just go to MailSealer > S/MIME Certificates > Private End-User Certifiates > Add > public certificates, then browse for the pem file (that contains all certificates and keys in pem format) and confirm with save.
Certificates are checked for validity when they are added (Validity period, Revocation Lists, Certificate Chain) and when they are used for incoming or outgoing E-Mails.
The following Trust States for root certificates are possible:
Normal: The certificate is checked for validity/trustworthiness
Untrusted: The certificate is not checked. It is not trustworthy.