Hi dikshagoel
Deliverability Rules and reputation building is done to ensure that email clients do not identify incoming emails as Spam.
This is the prime reason why we suggest such reply-to or sender addresses to be delegated with Adobe, since proper Deliverability checks are carried out for them.
In case of personal email addresses, email clients might qualify emails as Spam.
Quarantine is different from Spamming.
A Recipient's email address gets added to Quarantine List if that was non-contactable upto 5 tries, i.e. 5 consecutive Bounces.
Hope that clarifies!