Hi Hani -
What it sounds like might be happening is the email address that you are using as your "From" email address is getting marked as Spam or looks like you are sending a Spoofing email. Since the emails are coming out of a Cvent server but shows a different (non-Cvent email) address, some client email servers may recognize it and mark it as risky and reject it (which sounds like what might be happening).
Over the last couple of years, customer IT teams have added additional email security settings and many agencies have had to implement a DMARC (Domain-based Message Authentication, Reporting, and Conformance) process to more easily allow emails to pass through firewalls and reach the intended recipients.
You may want to see if there is a different email address you can use or if this is a customer whose email you will be using across a lot of events, it may be worth exploring with their IT Team on implementing a DMARC process.
Here are a couple of articles that can further explain how DMARC works and some options for adjusting:
https://support.cvent.com/s/communityarticle/Adding-or-Removing-Account-Email-Addresses?is_article=true&lang=en_US&searchFor=email%20spoofing
https://dmarc.org/wiki/FAQ#How_does_DMARC_work.2C_briefly.2C_and_in_non-technical_terms.3F
Contacting Cvent Support, they can also help you better understand the DMARC process.
Hope this helps!
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Rebecca Yousif
Senior Administrator
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