Sometimes, you'll never want any emails to sync from the inbox to an account. An example is if you have investors and you want to have the contacts in CRM for marketing purposes, but not to sync emails from the inbox.
To protect against this, you can do the following:
Add a custom field with any name (eg: Email_Sync_Blacklist__c)
Then update the Formula field in the field
Account.truly_emailDomain__c
To selectively reference the Blacklist Field. For example,
if(Email_Sync_Blacklist, '', if(find("/",if(find("www.",Website)>0,IF(FIND("//",Website)>0,substitute(Website,left(Website,find("//www.",Website)+5),NULL),Website),IF(FIND("//",Website)>0,substitute(Website,left(Website,find("//",Website)+1),NULL),Website)))>0,left(if(find("www.",Website)>0,IF(FIND("//",Website)>0,substitute(Website,left(Website,find("//www.",Website)+5),NULL),Website),IF(FIND("//",Website)>0,substitute(Website,left(Website,find("//",Website)+1),NULL),Website)),find("/",if(find("www.",Website)>0,IF(FIND("//",Website)>0,substitute(Website,left(Website,find("//www.",Website)+5),NULL),Website),IF(FIND("//",Website)>0,substitute(Website,left(Website,find("//",Website)+1),NULL),Website)))-1),if(find("www.",Website)>0,IF(FIND("//",Website)>0,substitute(Website,left(Website,find("//www.",Website)+5),NULL),Website),IF(FIND("//",Website)>0,substitute(Website,left(Website,find("//",Website)+1),NULL),Website))))
and set this to 'true'