Added max_msg_size startup parameter.

src/sbbs3/mailsrvr.c

@@ -1886,6 +1886,15 @@ static void smtp_thread(void* arg)
 
 				length=filelength(fileno(msgtxt))-ftell(msgtxt);
 
+				if(startup->max_msg_size && length>startup->max_msg_size) {
+					lprintf("%04d !SMTP message size (%lu) exceeds maximum: %lu bytes"
+						,socket,length,startup->max_msg_size);
+					sockprintf(socket, "552 Message size (%lu) exceeds maximum: %lu bytes"
+						,length,startup->max_msg_size);
+					subnum=INVALID_SUB;
+					continue;
+				}
+
 				if((msgbuf=(char*)malloc(length+1))==NULL) {
 					lprintf("%04d !SMTP ERROR allocating %d bytes of memory"
 						,socket,length+1);