[ZendTo] Linux newbie here - unable to send email to external email addresses.

[Chris Caylor]

Hello all!  New linux guy here and Zend.To is my second linux project to get going here at the city. I set up Zabbix monitoring a couple months ago and have those emails going out to our external email addresses so I know I'm doing some things right.
And Zend.To I have internal emails going to internal users when I set it up to send with no authentication, and I have of course tried the exact same port, encryption TLS, and exchange account and password, and every other combo.
I'm trying to work through the PHPmailer troubleshooting, but honestly a lot of it is over my head...

Here is the error I get when SMTPdebug is active.

2021-02-24 23:59:28 SERVER -> CLIENT: 220 mailserver.my.domain Microsoft ESMTP MAIL Service ready at Wed, 24 Feb 2021 15:59:28 -0800
2021-02-24 23:59:28 CLIENT -> SERVER: EHLO zendtoserver.my.domain
2021-02-24 23:59:28 SERVER -> CLIENT: 250-mailserver.my.domain Hello [10.1.10.70]250-SIZE250-PIPELINING250-DSN250-ENHANCEDSTATUSCODES250-STARTTLS250-X-ANONYMOUSTLS250-AUTH NTLM250-X-EXPS GSSAPI NTLM250-8BITMIME250-BINARYMIME250-CHUNKING250-XEXCH50250-XRDST250 XSHADOWREQUEST
2021-02-24 23:59:28 CLIENT -> SERVER: STARTTLS
2021-02-24 23:59:28 SERVER -> CLIENT: 220 2.0.0 SMTP server ready
SMTP Error: Could not connect to SMTP host.
2021-02-24 23:59:28 CLIENT -> SERVER: QUIT
2021-02-24 23:59:28 SERVER -> CLIENT:
2021-02-24 23:59:28 SMTP ERROR: QUIT command failed:
SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting

Thanks for your time!
Chris
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