Emails sometimes don't send and I see "Sending Message"
Over the past 6 months, I've had times when emails would not send and I discover that "Sending Message" or "Sending Messages" followed by a size - right now it's 516k, but it can be hundreds of Mb's. I've called support in the past and they've walked me through a process that ended up clearing this up and emails started flowing again. But, I've never been able to remember exactly what they did - had me do. I'm now "out of" support time and hoping someone in an Apple Community can help.
Using MacOS Catalina ver 10.15.7
iMac 21.5″, macOS 10.15