Generate EML file format from an Office Outlook email

EmailTools.ts

import { Buffer } from "buffer";

var item: Office.MessageRead;
Office.onReady(() => {
  item = Office.context.mailbox.item;
});

/**
 * Gets the email in EML format (IMF text file). This function executes the following steps:
 * (1) item.getAllInternetHeadersAsync()
 * (2) extract MIME boundary from headers to separate messages
 * (3) item.body.getAsync(Office.CoercionType.Html) & base64 encode
 * (4) item.body.getAsync(Office.CoercionType.Text) & base64 encode
 * (5) iterate through item.attachments & item.getAttachmentContentAsync()
 * You can do what you want with the file (string) once complete.
 * Note that this code does not encode the attachments into the file.
 * @param options - An object literal that contains one or more of the following properties:-
 *        `asyncContext`: Developers can provide any object they wish to access in the callback function.
 * @param callback - Optional. When the method completes, the function passed in the `callback` parameter is called with a single parameter,
 *                `asyncResult`, which is an `Office.AsyncResult` object.
 *                On success, the internet headers data is provided in the `asyncResult.value` property as a string.
 *                Refer to {@link https://tools.ietf.org/html/rfc2183 | RFC 2183} for the formatting information of the returned string value.
 *                If the call fails, the `asyncResult.error` property will contain an error code with the reason for the failure.
 */
export const getEmailContentAsync = async (
  options: Office.AsyncContextOptions,
  callback?: (asyncResult: Office.AsyncResult<string>) => void
) => {
  await item.getAllInternetHeadersAsync(
    options,
    await callbackWrapper(options, callback, async (headerResult) => {
      let header = headerResult.value;

      if (!header) {
        let headers = [`From: ${item.from.displayName} <${item.from.emailAddress}>`];
        if (item.to && item.to.length)
          headers.push(`To: ${item.to.map((e) => `${e.displayName} <${e.emailAddress}>`).join(", ")}`);
        if (item.cc && item.cc.length)
          headers.push(`CC: ${item.cc.map((e) => `${e.displayName} <${e.emailAddress}>`).join(", ")}`);
        headers.push(`Subject: ${item.subject}`);
        headers.push(`Date: ${item.dateTimeCreated.toUTCString()}`);
        headers.push(`Message-ID: ${item.internetMessageId}`);
        header = headers.join("\r\n");
      }

      await item.body.getAsync(
        Office.CoercionType.Html,
        callbackWrapper(options, callback, async (htmlResult) => {
          await item.body.getAsync(
            Office.CoercionType.Text,
            callbackWrapper(options, callback, async (result) => {
              const boundaryMatches = header.match(/boundary="([\w'()+,-./:=?]+)"/);
              const alternativeMatches = header.match(/Content-Type: multipart\/alternative;/);
              let boundary: string;

              if (boundaryMatches) {
                boundary = boundaryMatches[1];
              } else {
                boundary = `_${item.conversationId.substring(0, 68)}_`;
                header += `Content-Type: multipart/mixed;\r\n  boundary="${boundary}"\r\n`;
              }
              let messageBoundary = "_body_" + boundary.slice(6);

              if (alternativeMatches) {
                // Can skip multipart/mixed content-type header
                messageBoundary = boundary;
              }

              const body = result.value;
              const bodyHtml = htmlResult.value;
              let content = `${header}MIME-Version: 1.0\r\n`;

              if (!alternativeMatches) {
                content += `\r\n--${boundary}\r\nContent-Type: multipart/alternative;\r\n  boundary="${messageBoundary}"\r\n`;
              }

              content += `\r
--${messageBoundary}\r
Content-Type: text/plain; charset="utf-8"\r
Content-Transfer-Encoding: base64\r
\r
${base64Chunk(body).join("\r\n")}\r
\r
--${messageBoundary}\r
Content-Type: text/html; charset="utf-8"\r
Content-Transfer-Encoding: base64\r
\r
${base64Chunk(bodyHtml).join("\r\n")}\r
\r
--${messageBoundary}--`;

              item.attachments.forEach((a) => {
                content += `\r\n\r\n--${boundary}\r
Content-Type: ${a.contentType == "message/rfc822" ? "text/plain" : a.contentType}; name="${a.name}"\r
Content-Description: ${a.name}\r
Content-Disposition: ${a.isInline ? "inline" : "attachment"}; filename="${a.name}"; size=${a.size}`;

                // NB: This is where you would inline each attachment. I currently don't have need
                // to do this since I save attachments separately, but this is where you might do
                // item.getAttachmentContentAsync(a.id, options, ...);
              });

              if (!alternativeMatches) content += `\r\n\r\n--${boundary}--`;

              callback({
                asyncContext: options?.asyncContext,
                diagnostics: undefined,
                error: undefined,
                status: Office.AsyncResultStatus.Succeeded,
                value: content,
              });
            })
          );
        })
      );
    })
  );
};

// Base64 encode string and chunk into 76 char lines
const base64Chunk = (str: string): string[] => {
  let encoded = Buffer.from(str).toString("base64");
  let maxLength = 76;
  let result: string[] = [];
  while (encoded.length > maxLength) {
    result.push(encoded.slice(0, maxLength));
    encoded = encoded.substring(maxLength);
  }
  result.push(encoded);
  return result;
};

// Wrap callback in try/catch block
const callbackWrapper = (
  options: Office.AsyncContextOptions,
  callback?: (asyncResult: Office.AsyncResult<string>) => void,
  processSuccess?: (asyncResult: Office.AsyncResult<string>) => Promise<void>
) => {
  return async (asyncResult: Office.AsyncResult<string>) => {
    try {
      if (asyncResult.status != Office.AsyncResultStatus.Succeeded) {
        if (callback) callback(asyncResult);
        return;
      }

      if (processSuccess) await processSuccess(asyncResult);
    } catch (err) {
      if (callback) callback(wrapException(err, options.asyncContext));
    }
  };
};

// Wrap exception in asyncResult with Office error
const wrapException = (err, asyncContext?): Office.AsyncResult<any> => {
  let officeError = {
    code: 5001, // Internal error
    name: "getEmailContentAsync",
    message: undefined,
  };

  let asyncResult = {
    asyncContext: asyncContext,
    diagnostics: err,
    error: officeError,
    status: Office.AsyncResultStatus.Failed,
    value: undefined,
  };

  if (err instanceof Error) {
    officeError.name = err.name;
    officeError.message = err.message;
  }

  return asyncResult;
};

I wanted to document the way to call the code here (taken from @DevDuck's post to: https://techcommunity.microsoft.com/t5/microsoft-365-developer-platform/allow-msg-file-export-through-js-add-in-api-in-outlook-desktop/idc-p/3925786/highlight/true#M1969):

try {
  await getEmailContentAsync({}, async (asyncResult: Office.AsyncResult<string>) => {
    if (asyncResult.status != Office.AsyncResultStatus.Succeeded) {
      // handle error
      return;
    }

    let content = asyncResult.value;

    // upload file
    // Buffer.from(content, "utf8");
  };
}
catch (err) {
  // handle exception
}

Thanks again for creating this!

It looks like Microsoft has created a new method for doing this with the native Javascript API:
https://learn.microsoft.com/en-us/javascript/api/outlook/office.messageread?view=outlook-js-preview&preserve-view=true#outlook-office-messageread-getasfileasync-member(1)

Hi prmoore77
I am new to outlook add in development , i have to save the mail as .email file as you have mentioned here i used the same approach and same code that you have mentioned like this

try {
await getEmailContentAsync(
{},
async (asyncResult: Office.AsyncResult) => {
if (asyncResult.status != Office.AsyncResultStatus.Succeeded) {
// handle error
return;
}

    const content = asyncResult.value;
    const xx = JSON.stringify(content);
    console.log('content is :' + { xx });

    // upload file
    //Buffer.from(content, 'utf8');
  }
);

} catch (err) {
console.log('Error in saving file');
}

What ever content i am geting from this code that i am saving as .eml file but on opening the saved .eml file body part is block can you pls help me on this pls
Regards
Rajesh

i also want to get the outlook email in .eml file and upload on the server i am using getAsFileAsync

here is my code
Office.context.mailbox.item.getAsFileAsync({
},function(asyncResult) {
if (asyncResult.status === Office.AsyncResultStatus.Failed) {
return;
}
console.log(asyncResult.value);
});
it's not working