Validation Failed error message; can't send photos via LR

I had e-mailed photos from Lightroom for years prior to earlier this year (February 2022?). Since then I've received an error message entitled "Validation failed". It lists three things to check; 1) working internet connection (we have it) 2) anti-virus software might be blocking it (we've had the same anti-virus software for years), or 3) being on a corporate network - N/A. I've noticed many people raised this issue on various forums but I haven't seen a fix or solution yet. We use Hotmail as our server. Any advice?

<Moved from Lightroom Ecosystem to Lightroom Classic>