We currently encountered too many email bounces when we added around 45k new email addresses to the existing audience in smart list criteria.
I exported list of users from Marketo database and added the emails which were not included in the previous batches.
also, we are using the deliverabilty filters to the campaigns inorder to avoid the bounces -
Do you suggest something here as to how we can avoid the bounces?
Where are you getting these leads? I would look more critically at your data sources. Remember, it's against your Marketo TOS to email people who have not opted in (e.g. purchased list).
That said, there are email verification services like BriteVerify that you can use to scrub your list before adding to Marketo.