1>Is it possible to include the previous message during the email send from rollbase?
2> While sending the email to single contact, is it possible to select the contact email address
steps to reproduce
Click the single contact
Go to More action and send to
It doesn't select the email address of the contact
Seems like a bug to me, after clicking Send/Send To I believe the email should be pre-populated since you're already coming from the contact record.
For this type of requirement, I suggest you instead use a "Send Email" type of workflow action since you'll be able to preset the email(s) there as well as use an email template if you choose to.
Hope this helps.