S / MIME - when sending, the push button is sometimes not active, how to send an encrypted email?

Question

Encryption

I use S / MIME for encryption,
in the recipients I specify people who have a certificate and people who do not have a certificate (this is how it should be)
, sometimes it turns out to be sent to everyone, and sometimes the continue button is not active, and asks to delete people who do not have a certificate,
the question is, with what it's related?

Answer 1

Sending in this way is meaningless, unless the client is so smart that he first sends encrypted mail to those who have certificates, and then open mail to those who do not. Because if he is not so smart, then the client has two choices - send an encrypted letter to everyone (which those who do not have a certificate will not read) or send an unencrypted letter to everyone.
For example, when Outlook sees people with expired certificates in the list of recipients (that is, there are actually none), it asks - "send without encryption, send with encryption, but those without certificates will not read it, or what the hell is it, is this a letter?"
You didn't say what kind of client you have.