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How to Attach Multiple Files from URLs in Outlook for Workato Emails Using a Corporate Account

·Jul 30, 2026 11:59 PM·

Hi All. I have a recipe where a JSON list is submitted to the recipe of the details of a number of files. Each list item consisting of a fileName and an S3 pre-signedURL to the that file's content. I want to turn that list of files into email attachments and send them out. This works beautifully in "Mail for Workato". I just pass it the source list and choose "Use file URL" and it does all the work. Very cool. However, I need to use a corporate email account as the From address for this function (The recipients wonder why they are getting mail from mailer@au.workato.com and not our company domain) So I need to use the Outlook for Workato Send Mail action. That seems to work for everything except the attachments. It won't take the list of URLs and automatically download and attach them like Workato does. It insists on the attachment list having the actual binary content for each file. There is an Attachment URL option in the Outlook mailer, but that only allows for one file to be attached. I need all the files in the list to be attached. Has anyone found a way of dong this? I tried to create a list variable to hold the name and then read in binary content using Get File from URL, but Workato doesn't seem to want to allow a list element to have binary content. Strings, Integers, Numbers, Booleans etc. Yes. BLOBS, No. Any suggestions for workarounds would be appreciated!

5 comments

· Sorted by Oldest

Aaron W.
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Hey Evan! I'm tagging in Bill P. and Chris M. to take a look at this and will share it internally as well. Thanks so much for posting your question in the Community 🙂
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Chris M.
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evan.yates I'm going to "spitball" here in lieu of a confirmed solution. I suspect multiple file attachments is something we may ultimately need to raise with the platform team as a feature request. The first thing that jumps out at me is that it sounds like the downloaded files may be being stored in a format different from the original. In HTTP downloads (outside of Workato) you can specify a content-type in the request, and that defines the way the file is saved. Think text/html, image/jpeg, etc. So I'm wondering if this is an area to seek validation of the source and written file formats actually are. Second, if there's only an option to attach one file, perhaps you could zip the files into a single archive and attach that? The problem with this is that Zip files are seen as an attack vector and often rejected by the receiving email system. Another option might be to include the pre-signed URLs in the email body. This would allow the user to download the files directly, albeit I believe there is an expiration date on the URLs, which would prevent downloading if not done in a reasonable period of time. That creates more problems. Regarding Mail for Workato, I suspect our email address is used because we manage "Email Authentication" (SPF, DKIM, DMARC) to ensure delivery. We don't support custom email address likely due to the complexity of configuring email auth. This actually inspires my final idea. What about creating a custom action using Python and "rolling your own" email delivery agent? You could possibly relay email through your Microsoft org using SMTP Auth on a dedicated acoount, through an SMTP API if they offer one. Although this is fraught with some complexities, it might be possible. Lastly, I think this is worth bringing up with your Customer Success Manager, they might have suggestions I have missed, and it also helps to circulate product feedback. I'm happy to ideate here as well.
evan.yates
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Thanks for the reply, Chris. For most of your points, I have come to the same conclusion as you have in discarding the option.
ZIP files being junked/blocked by email services.
Including the URLs in the email body makes link expiry an issue.
I am hesitant to start developing custom code as the whole idea of adopting Workato was to make our workflow processing as low-code/no-code as possible. I'll try the Success Manager, but that means waiting for the slow gears to grind in their development backlog. I thought I'd ask the community if there was an easy answer first. Much appreciated.
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evan.yates
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Ok. I think I have solved my own issue. What I have done is loop through the list of attachments and turned them into a Workato list variable of file_name and file-contents using the Get file from URL. The trick is that I convert it to base64 text using a Ruby .encode_base64 before adding it to the list variable. Then when it comes time to send the email I specify the binary contents for each attachment as the list item .decode_base64
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Aaron W.
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Evan. Thank you so much for coming back to share your answer. Future folks with similar issues will be saved by you contributing this.