Hi JHyldgaard,
Currently, we have seen several threads reporting the problem:
When sending emails in Outlook for Mac 2011, if the attachment size is over 5MB, the email cannot be sent, and the following error occur:
“Error 18500” or
“HTTP error. The Server cannot fulfill the request”
I am sorry for all the inconvenience it caused. We are already aware of this issue and have reported it to the related team.
And once there is any update, we will share in the forum.
Once again, we sincerely apologize for the inconvenience this case has caused.
Your patience and understanding will be highly appreciated.
In addition, I have sent you a PM to collect some information from you, please refer to the steps below to read the PM and reply to it:
1. Go to "Your details" section on the right side of the community site
2. Click Private messages.
3. Click the subject title of the response to read the message.
The information will help us analyze this issue. I appreciate your time and efforts on this issue.
Best Regards,
Henry Huang