Since legal invoices are communications between lawyers and clients that may reveal an attorney’s strategy or legal advice, some states consider them to be privileged.  Therefore, law firms should check with their state bar association to determine what they need to do when emailing privileged information to clients, as those requirements could apply to emailed invoices as well.
Most billing and accounting programs (legal or general) have the capability to email invoices to clients directly from within the program. In many cases, that can be a batch activity.
Even if your program cannot email an invoice directly to the client, these programs typically allow users to download invoices as a PDF file, which law firms can attach to an email sent through the firm’s regular email program.
Keep in mind, email may not be the only option when electronically sending invoices. There are other secure electronic delivery methods such as the client portal.
1. CALIFORNIA SUPREME COURT: PRIVILEGED ATTORNEY INVOICES MAY LOSE PROTECTION ONCE LITIGATION IS OVER
2. Redacting Legal Invoices – The Attorney-Client Privilege and Attorney-Work Product Doctrine (Section 305) – Privileged Records
3. CASEMINE Search Results: billing records attorney client privilege
4. [Video] Quickbooks Online – How to CREATE / SEND INVOICE | 2018