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Sending Email Replies (Including Attachments) from Power Apps via Power Automate

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Posted on by CU25110357-0

I am working on recreating core mail functionalities inside a Power App. Users need to be able to send replies, modify CC recipients, and include attachments directly from the app.

As part of this, I need to trigger a reply that appears correctly under the original (parent) email thread. To do this, I need to obtain the exact Message ID of the source email so that the reply is threaded properly.

However, I am encountering two major issues:

The “Send a Reply (V3)” action in Power Automate is repeatedly failing with a Bad Gateway error. I am unsure whether this is a known limitation or a configuration issue.
I also need to send multiple attachments with the reply. These files will be uploaded from Power Apps and passed into the flow. I am looking for the correct approach to dynamically handle any number of attachments in a reply action.

I would appreciate guidance or examples of flows that address the following:

Retrieving the correct Message ID needed for threading.
Working around or resolving the Send a Reply (V3) Bad Gateway issue.
Structuring a flow that accepts and sends multiple attachments from Power Apps as part of the reply.

Thank you in advance for any help or best-practice recommendations.

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Pstork1 69,417 Most Valuable Professional on at

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Not sure how to get the message ID. It depends on where you are loading the message from for Power Apps. It should be in the header somewhere.

For the Reply error could you show how you have the action configured and the full error message.

For the multiple attachments I would suggest the following:

1) Create a Collection of attachments in Power Apps

2) Use JSON() to pass the collection as a JSON string to the flow

3) In the flow run Parse JSON on the attachment collection to be able to use the array in the flow

4) Add the array from the ParseJSON to the email after you switch it to accept an array of files

The array will need to have at least one file of the email will fail.

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CU25110357-0 2 on at

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I tried to create a collection of attachments and send them by email. Although the email was sent successfully, the file formats were always corrupted and could not be previewed. When sending the attachments, I used JSON.IncludeBinary, but I was never able to retrieve the actual contentBytes.

I also tried using Reply to email, but it consistently returned Internal Server Error or Bad Gateway errors. Later, I used Send an email, which worked, but it did not meet the requirement of replying to the original message.

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