Ignore received SMTP messages when the sender disconnects before the

acknowledgement ("250 OK") can be sent. In this case, the sender is either a
spammer or it is a legitimate delivery attempt that has been aborted for some
reason (e.g. timeout due to throttling).

src/sbbs3/mailsrvr.c

@@ -2461,6 +2461,11 @@ static void smtp_thread(void* arg)
 				lprintf(LOG_INFO,"%04d SMTP End of message (body: %lu lines, %lu bytes, header: %lu lines, %lu bytes)"
 					, socket, lines, ftell(msgtxt)-hdr_len, hdr_lines, hdr_len);
 
+				if(!socket_check(socket, NULL, NULL, 0)) {
+					lprintf(LOG_ERR,"%04d !SMTP sender disconnected (premature evacuation)", socket);
+					continue;
+				}
+
 				stats.msgs_received++;
 
 				/* Twit-listing (sender's name and e-mail addresses) here */