Added new account to Apple Mail, it can't authenticate though webmail works fine

I'm out of ideas on what to try here. 2018 MBP running Mojave 10.14.6. I just received a new work email address, that was just created and has never been used before. I have numerous other email addresses on this machine including Gmail, iCloud (me.com), and personal domains that all work perfectly well using IMAP/SMTP. This address just refuses to authenticate. The password is correct, everything is correct and in fact works perfectly at the host's webmail portal (hosts.co.uk). Specifically in Connection Doctor I get: WROTE Jan 15 17:42:49.136 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:imap.hosts.co.uk -- port:143 -- socket:0x600002192100 -- thread:0x6000050c7a00 8.1138 LOGIN my_login_id ******** READ Jan 15 17:42:59.137 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:imap.hosts.co.uk -- port:143 -- socket:0x600002192100 -- thread:0x6000050c7a00 8.1138 NO [AUTHENTICATIONFAILED] Authentication failed. WROTE Jan 15 17:42:59.137 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:imap.hosts.co.uk -- port:143 -- socket:0x600002192100 -- thread:0x6000050c7a00 9.1138 LOGOUT I've tried everything I can think of including manual (Advanced) settings for port, different SMTP account selections, enabling "less secure apps" on Google (since I'd like to use them for SMTP), confirming Google's "I'm really me" CAPTCHA, and a host of other stuff I can't even remember at this moment. This is my only address that fails to work, and in fact the only address I've ever had not "just work" and I've been using Mail since the beginning. Any suggestions?