keychain password problem
Inexplicably, I am unable to send messages on my iMac using one of my two email accounts. When i try to send the message I am told "Mail wants to sign using key 'privateKey' in your keychain," and that "To allow this, enter the 'login' keychain password." Forgive my cluelessness, but I have no idea what this means, nor how to proceed.
iMac 21.5″, macOS 10.13