What about a Buffer full message?
Editor.c of swfotefuss:
if( TOTAL_BUFFER_SIZE( edd ) + linelen + 2 >= edd->max_size )
send_to_char( "Buffer full.\r\n", ch );
editor_save( ch, edd, "" );
I tried to fill up a mail note and got that. I'll dig some more, but take a peek at your mail file and see if there is something missing.