Mail can't connect to Gmail SMTP server

I recently updated my Mac Pro from Sierra to High Sierra and now Mail cannot connect to the Gmail SMTP server. So I can receive mail but I cannot send. I have found posts from many other users with the same problem and none of the solutions have worked for me. I have tried deleting prefs, deleting my Gmail account in Internet Accounts, turning on and off two step verification, and nothing has worked. When I run Connection Doctor, I see the following in the error log: WROTE Mar 07 10:32:09.713 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:smtp.gmail.com -- port:465 -- socket:0x6140004a3060 -- thread:0x600000267340 EHLO vuze on mac-pro.home READ Mar 07 10:32:09.749 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:smtp.gmail.com -- port:465 -- socket:0x6140004a3060 -- thread:0x600000267340 501-5.5.4 HELO/EHLO argument "vuze on mac-pro.home" invalid, closing Oddly, when I open terminal the command prompt says "vuze on Mac-Pro:". So this makes me think the problem is something OS or network related, but I have no idea where to start. Any ideas?