Mail won't send

When I send a message to a number of people I often get the warning that says: " does not appear to be a valid email address. Verify the address and try again. (That quote isn't mine. The message says it's the quotation mark that isn't valid. There is never a quotation mark in any of the addresses. The only solution is to send the message is smaller batches until I find the address that's holding up the transmission. When I find that address it never has a quotation mark in it. The solution winds up being very time consuming and I learn nothing. I have to choose an OS to ask this question but the options don't include Ventura. So instead I have to choose what is giving me the problem, but Mail isn't an option. I tried picking App as the issue, but the listing under that doesn't include Mail. So I hope it gets to Apple to update its community help page. I'll just go ahead and select Mojave. It wasn't working right then, either.).