Exchange 2013 Mail Relay from External Web Service

CMCITD
CMCITD used Ask the Experts™
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All of our mail relaying for notifications are done internally.  Our web host is wanting to relay mail for job application submissions to our HR Department.  They are using http://demotesturl.com/smtp/ to test the SMTP settings I provide them, but fails?  I have created a mail relay user in exchange with a password but still no luck.  I can send an email from an external email client via telnet tho?

Normally from withing the Exchange 2013 Admin Center I will just add the internal IP addresses to a receive connector I have configured to allow internal servers to relay mail for alerts.  Would this be the same for an outside vendor/service?

Is there anywhere I can see logs as to why this is failing or where to double check the configurations?
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IT Architect
Distinguished Expert 2017
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Ask your vendor to relay via internet and use its own SMTP server to relay mails.

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