a gdb run with symbols and debugging enabled shows Program received signal SIGSEGV, Segmentation fault. [Switching to Thread 182912014688 (LWP 29007)] 0x000000000042d14a in vbuf_print (bp=0x56ead8, format=Variable "format" is not available. ) at vbuf_print.c:196 196 VBUF_STRCAT(bp, s); (gdb) bt #0 0x000000000042d14a in vbuf_print (bp=0x56ead8, format=Variable "format" is not available. ) at vbuf_print.c:196 #1 0x0000000000429d3c in vstring_vsprintf (vp=0x56ead8, format=Variable "format" is not available. ) at vstring.c:485 #2 0x000000000040e354 in vlog_adhoc (id=0x56aa88 "160581ACFD4", orig_rcpt=0x56a968 "Petertgvf@vip.0451.com", recipient=0x56ad28 "Petertgvf@vip.0451.com", relay=0x56b708 "mail.vip.0451.com[210.76.63.138]", entry=Variable "entry" is not available. ) at log_adhoc.c:117 #3 0x000000000040c355 in vbounce_append (flags=0, id=0x56aa88 "160581ACFD4", orig_rcpt=0x56a968 "Petertgvf@vip.0451.com", recipient=0x56ad28 "Petertgvf@vip.0451.com", offset=140, relay=0x56b708 "mail.vip.0451.com[210.76.63.138]", entry=5684824, fmt=0x56b1d8 "\b²V", ap=0x7fbffff720) at bounce.c:262 #4 0x000000000040a1e9 in smtp_rcpt_fail (state=0x56aea8, code=550, rcpt=0x564c98, format=0x42e430 "host %s said: %s (in reply to %s)") at smtp_trouble.c:334 #5 0x00000000004082b8 in smtp_xfer (state=0x56aea8) at smtp_proto.c:906 #6 0x0000000000406d0d in smtp_connect (state=0x56aea8) at smtp_connect.c:628 #7 0x0000000000405e95 in deliver_message (request=0x56a108) at smtp.c:399 #8 0x0000000000405ef1 in smtp_service (client_stream=0x568fd8, unused_service=Variable "unused_service" is not available. ) at smtp.c:432 #9 0x000000000040b26d in single_server_wakeup (fd=Variable "fd" is not available. ) at single_server.c:250 #10 0x000000000040b390 in single_server_accept_local (unused_event=Variable "unused_event" is not available. ) at single_server.c:292 #11 0x0000000000422d1b in event_loop (delay=-1) at events.c:591 #12 0x000000000040bd69 in single_server_main (argc=Variable "argc" is not available. ) at single_server.c:639 #13 0x000000000040608c in main (argc=Variable "argc" is not available. ) at smtp.c:586