Large file attachment issue

Hi @R, Pandi Priyanga (Cognizant) ,
Thanks for visiting our forum, here we mainly focus on general issues about Outlook desktop client.

Seems that you were trying to edit emails with large attachment and found that you could not download this attachment from emails in the Outlook Draft folder before sending out, right?

I am sending pdf as base64 encoded format for attaching large files using upload session, not able to download the attached pdf properly from outlook mail draft.

What is the specific size of your large attachment?
How did you add the large attachment, edit and download the attachment from emails? Via Outlook desktop client (such as Outlook 365) or using other programming ways?
If you were not using Outlook desktop client, to further confirm your issue, it is suggested for you to do the same operations in Outlook client and see if the issue has any difference.

Are there any error prompts when this issue occurs?
To confirm if your issue is related to this email message itself, please try to log in your web mail and download the attachment to see if the issue could be reproduced.

If you have any update about this issue, please feel free to post back.

If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.