You can automatically email transactions to Customers, which will be sent on creation and update.
Note: If you do not want to use this functionality, then make sure the below settings remain unchecked.
The delivery preference you define below will default on all new customer records you create:
1. Go to Setup.
2. Click Company.
3. Click Email Preferences.
4. Check Customer default to Email Transactions.
5. Click Save.

Customers have preferences for how to receive transactions, you can set preferred default transaction delivery methods on customer records.
1. Go to Info.
2. Check Email.
3. Click Save.

Note: You can also set these fields on the Customer record using the Mass Update function. Go to Lists > Mass Updates > Mass Updates > General and click Customer.
Email Transaction for a specific Transaction type
If you only want transactions to be emailed for one transaction type, for example an Invoice. Please follow the below steps on how to customise the form.
Navigate to your Invoice, click Edit > Customise > Customise Form.

2. Click Screen Fields.
3. Click Messages.
4. Change To Be Emailed check box default to Checked.
5. Click Save.
