Avoid Exceeding Soft Private Memory Limit When Receiving Email

What do I have:

I configured GAE to receive email, remove attachments and store it in a blockblock, then send the mail.

Problem:

When GAE receives mail from gmail with attachments larger than 5MB, it throws an "Out of soft memory" error (I think GAE can receive email with attachments up to 10MB).

What i know

As per the link What is "Limited Private Memory" in GAE? I need to increase my frontend and backend instance class so that the memory quota can be increased.

What I need

I need to know if there are any things that might be missing, or any idea to work with emails that have attachments up to 10MB. All I have to do is detach the attachments from the email and save to the block store, then send the email using blob keys generated with the same. The workflow works fine for up to 5 MB attachments, but does not work for large attachments up to 10 MB.

Any help would be appreciated. Let me know if you need more information. Thank!