By default IBM® Lotus® iNotes™ allows a maximum attachment size of 50,000K (50MB). You can increase this amount by setting the "Maximum attachment size (kb)" field in the Domino server Configuration Settings document, Lotus iNotes tab. However, attachment size is based on two parameters that default to a 10,000K (10MB) limit independent of this setting. So even though Lotus iNotes allows for a larger attachment, the following two settings must be increased to a value larger than the Lotus iNotes maximum attachment setting for users to be able to add attachments larger than 10MB.
In the Server or Web Site document, set these settings higher than the Lotus iNotes "Maximum attachment size" field:
- In the Server document - Internet Protocols - HTTP - Maximum Size of Request
- In the Server or Web Site document - Internet Protocols - Domino Web Engine - Maximum Post data
From: https://www.ibm.com/support/knowledgecenter/en/SSKTMJ_8.5.3/com.ibm.help.domino.admin85.doc/H_SETTING_A_MAXIMUM_ATTACHMENT_SIZE.html