Thanks.
26 answers
Ok..finally the answer.
First, create two custom fields on the account:
LastEmailDate (date)
LastEmailTo (email)
Step2: Create PB on Email Message
Criteria is:
RelatedToID starts with ID 001
Update Related Records: Relatedto Account
LastEmailDate formula Today()
LastEmailto field reference EmailMessage.ToAddress
Step3: Create PB on Account
Criteria is:
LastEmailDate = Today()
LastEmailto is null boolean false
Update Related Records: Contacts
Critiera for update:
Email = Account.LastEmailTo
Field Update
Update your checkbox