I downloaded the new version of Thunderbird Mail, and now, I'm having continual trouble sending messages (but no trouble receiving them). A pop-up window keeps appearing requiring me to re-sign into my Microsoft account, for some reason, but whenever I press "continue" to sign in, nothing happens, and selecting "cancel" also has no effect. I'm already signed in to my Microsoft account on my laptop, anyway, so I don't know why this window keeps appearing, but I assume it's related to the fact that I'm having trouble sending e-mail. I have to keep closing the Thunderbird program and re-opening it every time I want to send new messages. This is becoming very tiresome. I've already tried closing and re-opening the Thunderbird program, but that doesn't fix the problem. I'm working on a Mac, with the latest iOS. All suggestions appreciated!