The way you describe this is confusing.
- How do you know that they are not in Marketo? What did you check exactly?
- Does the Marketo User see all the SFDC leads?
- Did you delete some records in either system?
- Hard Bounces or email flags don't usually affect the sync unless you setup the Marketo to SFDC lead process to do so.
1) I created a smart list with the Email address filter and found that there are some emails missing in the leads tab, also I have checked in Marketo Lead Database but still no luck.
2) I didn't get your question
3) I am not sure exactly, but is there a way to get those lead deleted details
4) Thank you for the information, I will check with that.