To alleviate the "error writing message: File too large", Postfix error, it is possible to increase the mailbox size limit parameter in main.cf.
You can check with postconf: postconf | grep mailbox_size_limit
It is possible you won’t have mailbox_size_limit explicitly set. postconf might be displaying the default value. It is defined in /etc/postfix/main.cf. The default setting looks like this: mailbox_size_limit = 51200000. The size is in bytes. Zero is unlimited.
To set it to your desired size, add the line mailbox_size_limit = 512000000 to /etc/postfix/main.cf with your preferred text editor, or run postconf postconf -e 'mailbox_size_limit = 512000000', where I just added a zero to increase the limit from 50 MB to 500 MB. Then reload Postfix: service postfix reload.
Postfix documentation: The maximal size of any local 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 delivery agent.
This limit must not be smaller than the message size limit.