Both Breadwinner and QuickBooks Online allow you to have multiple email addresses associated with a QuickBooks Online Company, and also to have multiple email addresses associated with each invoice.
And, these do not have to be the same. You might have email address A, B, and C on the QuickBooks Online Company, but at the time of Invoice creation, you might remove B and C and add in D and E. And, likewise, for another email it might be F and G.
Breadwinner has an email address field on the custom object QuickBooks Online Company in Salesforce, and it has an email address field on each Invoice record in Salesforce.
The only limitation is that the total character length of these fields must be 100 characters or less, and if there are multiple emails, they must be separated by a comma.
So, the following examples are valid values for the email address field.
email@example.com firstname.lastname@example.org, email@example.com firstname.lastname@example.org,email@example.com,firstname.lastname@example.org
Please keep in mind that the limit of 100 characters is set by QuickBooks Online. We cannot increase this.