I am using IIS 6 SMTP Virtual Server to relay messages from our internal network to Exchange Online. This is working correctly except for one minor problem.

When using Task Scheduler to send an email with attachment (using the built in send email function), the attachment cannot be opened. When attempting to open an excel file (.xlsx, or .xlsm) sent by a scheduled task, Excel states "The file is corrupted and cannot be opened", or "Excel found unreadable content in <filename.xlsm>". 

By monitoring the SMTP queue folder, I can see the Content-Transfer-Encoding is set to base64 for emails with attachments sent by our other automated systems. However, excel files sent by Task Scheduler are incorrectly set to 8 bit instead. This only seems to happen with Excel files. Files with .pdf or .docx extensions can be opened after being emailed by Task Scheduler.

My best guess is that this is a failing of the SMTP relay. Is there some way this can be configured to encode Excel attachments as base 64?

• Changed type Vivian_WangMicrosoft community contributor, Moderator 18 minutes ago

I would recommend asking them here: http://forums.iis.net/

Will do, thanks!

By the way, why is this proposed as an answer? When I search these forums and see a thread with the "Answered"  check mark, I am hopeful that reading that thread will give me the solution I am looking for. All too often, the post which was marked as an answer is not an answer at all, but a request for more information. This peculiar habit makes these forums less useful when looking for an answer.

Hi,

Thanks for your feedback.

Since the issue is related to IIS and i could not move it to IIS forums, so i will change the type from question to discussion. And you need to post it in IIS forums.

Thanks for your understanding.

Regards.