mail wants to sign using key "privateKey" in your keychain?

Hey ncbucki,

It sounds like you're possibly trying to send an encrypted email from the Mail app. If that's the case, there must be a personal certificate in your keychain. Here's more information: Sign or encrypt emails in Mail on Mac - Apple Support

Send digitally signed and encrypted emails

A digitally signed message lets your recipients verify your identity as the sender; an encrypted message offers an even higher level of security. To send signed messages, you must have a personal certificate in your keychain. To send encrypted messages, the recipient’s certificate must be in your keychain.

1. In the Mail app  on your Mac, choose File > New Message.

2. Move the pointer over the From field, click the pop-up menu that appears, then choose the account for which you have a personal certificate in your keychain.

A signed icon (containing a checkmark) is shown in the message header and indicates your message will be signed when you send it.

3. Address the message to recipients.

An encrypted icon (containing a closed lock) is shown if your keychain contains a personal certificate for every recipient. If you don’t have a certificate for every recipient, click the encrypted icon in your message; an open lock replaces the closed lock, indicating the message will be sent unencrypted.

Some mailing lists reject digitally signed messages because the signature is treated as an attachment. If this happens, click the signed icon in your message; an x replaces the checkmark, indicating the message will be sent unsigned.

Note: If for some reason your certificate isn’t associated with your email address, or if you want to use your certificate with a different email address, Control-click the certificate in Keychain Access, choose New Identity Preference, and provide the requested information.

Let us know how it goes.

Take care!