Trying to diagnose an issue with my mom's Macbook (running Yosemite). She is unable to send “new” emails. She can receive emails and repling to emails recipients can receive them, but something is amiss with “new” emails…even if sent to accurate email addresses. So, the outgoing and incoming servers seem to be functional. I've deleted the playlist in the library, and rebooted the system but that didn't seem to help.
Any suggestions ?