We are using marketo for our syncing with SFDC. We also have need to send individual emails non marketing, like payment confirmation etc.
Is there a method that can send the mails for an individual not a group or campaign.
Could you describe more clearly the steps you wish to take?
From your message it seems like you may want to use Marketo to send Billing Emails, Renewal Reminders, etc. Yes you can do this. It will depend alot on your SFDC and setup for Opps and Account data.
If you want that email to be physically in SFDC, then you should check off Email Send on SFDC>Sync items in admin.