How to auto-reply to customer emails in Outlook with AI Builder and Power Automate

Create a folder in OneDrive for Business (the video uses Email Support KB) and add the files the AI should answer from. The demo has five PDFs: business policies, customer support reference, product catalog, service offerings and a technical support manual.

The customer support reference file holds guidelines and standard response templates, which helps the AI match your house style. You can use as many files as you need, but the prompt needs one input per file.

In Power Automate, go to AI hub and select Prompts, then Build your own prompt. Paste your instructions. The video's instructions cover:

• Only respond to emails about product specifications, pricing, tech support, returns, warranty and similar customer topics
• Do not reply to internal company emails, personal conversations or marketing emails
• Search the knowledge base files, and only answer if they fully answer the question
• Tone, language, content and format guidelines, plus a response structure: greet professionally, acknowledge the question, give a direct answer with details
• A signature to add to every reply
• Output exactly no when the email should not get a reply or there is not enough information

That no rule is what the flow checks later.

Where the instructions mention the knowledge base, click Add content, select Image or document and name the input File 1. Repeat for File 2 to File 5.

Replace the email placeholders with Text inputs named Email sender, Email subject and Email body. Power Automate fills these inputs when the flow runs.

For testing, upload your five files into the file inputs and paste a sample email subject and body. Change the model to the standard GPT 4.1, which gave better answers than the default GPT 4.1 mini in the video. Click Test.

Try a support question, a product enquiry and an internal message such as a meeting reminder. The first two should get full replies built from your files, and the meeting reminder should return no. Name the prompt Customer email support and save it.

Go to Create, select Automated cloud flow, name it Customer email support, and pick the Office 365 Outlook trigger When a new email arrives (V3). The flow now runs for every email that lands in your inbox.

Add Get file content from OneDrive for Business. Rename it File 1, click the folder icon, open the Email Support KB folder under root and pick the first file. Add four more Get file content actions for the other files, named File 2 to File 5.

Add Run a prompt from AI capabilities and select Customer email support. The inputs may appear in a different order, which is fine because they are named. Map them:

• Email body: Body from the trigger
• Email subject: Subject from the trigger
• File 1 to File 5: File content from the matching Get file content action
• Email sender: From from the trigger

The sender is optional, but it gives the AI more context.

Save, click Test, choose Manually, and send a test email to the mailbox. When the run finishes, open Run a prompt, select Show raw outputs and find the text in the body. The reply is good, but the line breaks show as \n characters. If you drop that text straight into an HTML email, the breaks disappear and the reply becomes one block.

Edit the flow and add Initialize variable. Name it Line breaks, set Type to String, click in Value and press Enter once. The value is simply a new line. You will swap each new line for an HTML <br> tag in the reply body.

Add a Condition. On the left, pick the Text output from Run a prompt. Choose is not equal to and type no on the right. Everything that should get a reply goes into the True branch. Internal emails and questions the files cannot answer go to False, where nothing happens.

In the True branch, add Reply to email (V3). Set Message Id to the trigger's Message Id. Open Advanced parameters and add Body (you can also add CC or BCC here).

For Body, open the expression editor and build:

replace(outputs('Run_a_prompt')?['body/responsev2/predictionOutput/text'], variables('Line breaks'), '<br>')

Type replace(, pick Text from Run a prompt in the dynamic content (Power Automate inserts the reference for you), add a comma, pick the Line breaks variable, add a comma and '<br>'. This replaces every new line with an HTML break.

Add Assign an Outlook category. Set Message Id to the trigger's Message Id and type AI replied as the category. You can now see in Outlook which emails the flow answered.

If you would rather check each answer first, use Draft an email message instead of Reply to email (V3). The flow then saves a draft with the AI text, and the category tells you which drafts to review.

Save and test again. Send a support question and check that a reply with step by step instructions and your signature goes out, and that the original email shows the AI replied category. Then send a customer enquiry and an internal email one after the other. The flow should answer the enquiry from the product catalog and ignore the internal email.