Hi @EmilyLeDuc,
Welcome to the Community! Happy to help!
Klaviyo works best as a 1:1 sync and is designed to connect one account per one store/brand. So yes, using a different sender email and reply to address would result in deliverability issues since a company’s sending reputation is developed over time through a combination or sending behavior and infrastructure. Inbox providers will typically mark an email as unverified or spam if they have different root domains for instance, because it doesn’t seem connected to your business.
If you are interested in sending an email from a different email address manually, I would ensure that the root domain remains the same if you want to create an email that looks like it’s coming from the owner. Therefore this would help signal to inboxes that they could trust this email because it’s connected to the root domain of your existing brand.
However it should be noted that this is a suggestion as we can’t ultimately control where an email lands in the inbox!
Hope this helps!
-Taylor