Anybody else on the forum uses Dreamhost. I haven’t been able to send emails for I don’t know how long. At this point, I don’t know if it’s Dreamhost or eM Client.
According to Reddit posters, it seems Dreamhost (some people on Reddit call it NightmareHost) has long had issues in various areas, including email hosting. I would consider finding a different email provider, one with better email hosting reliability and eM Client support.