Webform unable to send email – SMTP auth test does send

As the subject says, I have an old site that was functioning properly…not sure when it went south.

SMTP auth settings are as follows: SMTP server is onsite exchange, port 25, no encryption, no auth. No errors and the email is sent as desired.

https://i.imgur.com/mDulEnY.png

When attempting to submit, this error is thrown and no email is sent.

https://i.imgur.com/iXO10JV.png

I can’t find anything in the webform itself that seems pertinent.

Any ideas? I’m a total Drupal noob, please consider if responding.

Thanks!

Drupal version: 


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