I have a question regarding the S/MIME. We have an email address which has assigned the Exchange Online Plan1 license. But recently we have the problem that many incoming emails to this mailbox can not be read regarding S/MIME. The error output looks like SEPPmail domain ecnryped message. Even with the Microsoft SMIME extension and the domains specified in it, this does not work. This is only the case with this one email address. I also used Exchange Remote Powershell to look at the setting and for all email addresses, the UserSMimeCertifiate and UserCertifiate field is empty.
I would need urgent help here as important emails are arriving there.