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Attachment issue: attachments received as winmail.dat files


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When customers are emailing attachments, they are being received as .dat attachments.

The following file formats are affected (that I know of):

  • xlsx
  • eml
  • jpg
  • png
  • docx
  • pdf

Is anyone else experiencing this issue?

Attachments that arrived yesterday from customers are okay.

Many thanks,

DAT attachment.png

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@Alisha it's possible the sending clients are using Rich text rather than HTML or plain text format for their outbound emails, see the following which discusses how to turn off the TNEF format to ensure better compatibility.  It might be worth giving this a try for one Outlook client to see if it makes a difference:



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Hi @Deen,

Thank you for your quick reply.

I have tried sending 3 test emails - one Rich text, one Plain text, and one HTML - all with the same JPG attachment, but all of them have arrived with the DAT attachment.

Many thanks,

Plain Text.jpg

Rich Text.jpg

HTML Text.jpg

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@Alisha you would need to take this with your mail server admins or people that look after email in your organisation to look at. Unfortunately, there is nothing that Hornbill can do, we simply cannot decode or decipher emails that have RTF or TNEF format. It is possible that even if you changed the formatting in your email client, the mail server is configured to automatically change the formatting to RTF for certain emails as such overwriting your formatting from the client. However, this is something that only your admins can advise on...

Here is an example of the exact same issue occurring in a different product that Hornbill which shows how the issue occurs and shows that there isn't a defect or something working incorrectly (not as designed) in Hornbill: https://community.spiceworks.com/topic/1977092-contact-receiving-attachments-as-winmail-dat

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  • Victor changed the title to Attachment issue: attachments received as winmail.dat files

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