Setting Up Reply Email for Our New Newsletter: Need Guidance

Hi Hiiv! I'm setting up a new newsletter https://psychiatry30.beehiiv.com/ that will end up either being on a custom subdomain blog.noesisclinic.com or as a subpage www.noesisclinic.com/blog. My question is regarding the "reply email" custom set up. I want to keep a buffer so that patients do not end up using the newsletter "reply" email as a backdoor/alternative communication channel for medicine refill requests, clinical updates, etc. We do not use email with our patients. So I was trying to set up an 'alias' email with our custom domain 'newsletter [at] noesisclinic.com' that is an alias for one of our office admin emails. However, beehiiv wasn't able to send a 'verify your reply to' email to this alias address. When I used the official administration microsoft business 365 email with our clinic domain [at]noesisclinic.com that worked. Does this have to do with DMARC authentication? I'm having a web developer team update our website for the office noesisclinic.com and they are going to link beehiiv to our main website (either as a subdomain or a subpage) and I need to figure out which 'reply to' email to use. There was also a note that DMARC emails will get flooded with status updates so use a throwaway email? I didn't understand that part. Thank you for your help in understanding the nuances here.