message_size_limit (default: 10240000)
The maximal size in bytes of a message, including envelope information.
Note: be careful when making changes. Excessively small values will result in the loss of non-delivery notifications, when a bounce message size exceeds the local or remote MTA's message size limit.
mailbox_size_limit (default: 51200000)
The maximal size of any local(8) individual mailbox or maildir file, or zero (no limit). In fact, this limits the size of any file that is written to upon local delivery, including files written by external commands that are executed by the local(8) delivery agent.
This limit must not be smaller than the message size limit.