Hi Jane,
Sorry for the inconvenience the issue caused. Currently, we received several posts about the issue.
Symptoms:
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When trying to send email with attachments Outlook 2011 users are reporting the error "HTTP Error. The server cannot fulfill the request" Error code: -18500
If the attachments exceed 5-10mb in size then the email fails to send. If the attachments are under 4-5mb then it sends successfully.
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We have been aware of the issue, and the investigation is going on by the back end team. Once there is any update, we will update it in this forum.
Thanks for your understanding and patience.
Regards,
Johnny Zhang