Just wanted to share a "debug session" to trace down a "Mail loop detected"
situation:
A bounce mail with reason "Mail loop detected" is generated under this
circumstance:
if it takes too many steps (operations) to get the first MX record
(or the final A record when MX is missing after trying all)
of the recipient domain than what is defined in server.tab under
"MaxMTAOps" "16"
For example:
I had a mail to an address xx...@embarqnow.net and got that error
because that domain has many nameservers and a depth of 3 levels
to finally get the MX record, but the number of steps to get to the MX
exceeds the above defined 16 ...
#################################################
# dig embarqnow.net any
; <<>> DiG 9.8.1-P1 <<>> embarqnow.net any
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41501
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 13
;; QUESTION SECTION:
;embarqnow.net. IN ANY
;; ANSWER SECTION:
embarqnow.net. 39916 IN A 64.45.201.2
;; AUTHORITY SECTION:
net. 62167 IN NS f.gtld-servers.net.
net. 62167 IN NS d.gtld-servers.net.
net. 62167 IN NS b.gtld-servers.net.
net. 62167 IN NS i.gtld-servers.net.
net. 62167 IN NS g.gtld-servers.net.
net. 62167 IN NS k.gtld-servers.net.
net. 62167 IN NS a.gtld-servers.net.
net. 62167 IN NS e.gtld-servers.net.
net. 62167 IN NS j.gtld-servers.net.
net. 62167 IN NS c.gtld-servers.net.
net. 62167 IN NS l.gtld-servers.net.
net. 62167 IN NS m.gtld-servers.net.
net. 62167 IN NS h.gtld-servers.net.
;; ADDITIONAL SECTION:
a.gtld-servers.net. 22812 IN A 192.5.6.30
a.gtld-servers.net. 120523 IN AAAA 2001:503:a83e::2:30
b.gtld-servers.net. 2525 IN A 192.33.14.30
b.gtld-servers.net. 9837 IN AAAA 2001:503:231d::2:30
c.gtld-servers.net. 11423 IN A 192.26.92.30
d.gtld-servers.net. 79977 IN A 192.31.80.30
e.gtld-servers.net. 119385 IN A 192.12.94.30
f.gtld-servers.net. 70410 IN A 192.35.51.30
g.gtld-servers.net. 23788 IN A 192.42.93.30
h.gtld-servers.net. 23957 IN A 192.54.112.30
j.gtld-servers.net. 23958 IN A 192.48.79.30
l.gtld-servers.net. 22980 IN A 192.41.162.30
m.gtld-servers.net. 25511 IN A 192.55.83.30
;; Query time: 5 msec
;; WHEN: Fri Oct 12 16:20:56 2012
;; MSG SIZE rcvd: 500
#################################################
And picking one of the nameservers gives:
# dig @b.gtld-servers.net embarqnow.net any
; <<>> DiG 9.8.1-P1 <<>> @b.gtld-servers.net embarqnow.net any
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7771
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 2
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;embarqnow.net. IN ANY
;; AUTHORITY SECTION:
embarqnow.net. 172800 IN NS ns1.embarqservices.net.
embarqnow.net. 172800 IN NS ns2.embarqservices.net.
;; ADDITIONAL SECTION:
ns1.embarqservices.net. 172800 IN A 138.210.81.3
ns2.embarqservices.net. 172800 IN A 64.45.205.2
;; Query time: 97 msec
;; WHEN: Fri Oct 12 16:29:17 2012
;; MSG SIZE rcvd: 114
#################################################
And continuing:
# dig @ns1.embarqservices.net embarqnow.net any
; <<>> DiG 9.8.1-P1 <<>> @ns1.embarqservices.net embarqnow.net any
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61425
;; flags: qr aa rd; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 3
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;embarqnow.net. IN ANY
;; ANSWER SECTION:
embarqnow.net. 86400 IN SOA ns1.embarqservices.net. dns-admin.embarqservices.net.
2011070100 10800 3600 604800 86400
embarqnow.net. 86400 IN NS ns2.embarqservices.net.
embarqnow.net. 86400 IN NS ns1.embarqservices.net.
embarqnow.net. 86400 IN MX 10 localhost.embarqnow.net.
embarqnow.net. 86400 IN A 64.45.201.2
;; ADDITIONAL SECTION:
ns1.embarqservices.net. 10800 IN A 138.210.81.3
ns2.embarqservices.net. 10800 IN A 64.45.205.2
localhost.embarqnow.net. 86400 IN A 127.0.0.1
;; Query time: 130 msec
;; WHEN: Fri Oct 12 16:30:11 2012
;; MSG SIZE rcvd: 218
#################################################
The solution in this case would be to increase the above said limit in
server.tab.
OTOH the following command finds it immediately:
# dig embarqnow.net MX
; <<>> DiG 9.8.1-P1 <<>> embarqnow.net MX
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10491
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 13
;; QUESTION SECTION:
;embarqnow.net. IN MX
;; ANSWER SECTION:
embarqnow.net. 43200 IN MX 10 localhost.embarqnow.net.
;; AUTHORITY SECTION:
net. 60442 IN NS d.gtld-servers.net.
net. 60442 IN NS j.gtld-servers.net.
net. 60442 IN NS i.gtld-servers.net.
net. 60442 IN NS c.gtld-servers.net.
net. 60442 IN NS l.gtld-servers.net.
net. 60442 IN NS m.gtld-servers.net.
net. 60442 IN NS b.gtld-servers.net.
net. 60442 IN NS e.gtld-servers.net.
net. 60442 IN NS g.gtld-servers.net.
net. 60442 IN NS a.gtld-servers.net.
net. 60442 IN NS f.gtld-servers.net.
net. 60442 IN NS k.gtld-servers.net.
net. 60442 IN NS h.gtld-servers.net.
;; ADDITIONAL SECTION:
localhost.embarqnow.net. 38196 IN A 127.0.0.1
a.gtld-servers.net. 21087 IN A 192.5.6.30
a.gtld-servers.net. 118798 IN AAAA 2001:503:a83e::2:30
b.gtld-servers.net. 800 IN A 192.33.14.30
b.gtld-servers.net. 8112 IN AAAA 2001:503:231d::2:30
c.gtld-servers.net. 9698 IN A 192.26.92.30
d.gtld-servers.net. 78252 IN A 192.31.80.30
e.gtld-servers.net. 117660 IN A 192.12.94.30
f.gtld-servers.net. 68685 IN A 192.35.51.30
g.gtld-servers.net. 22063 IN A 192.42.93.30
h.gtld-servers.net. 22232 IN A 192.54.112.30
j.gtld-servers.net. 22233 IN A 192.48.79.30
l.gtld-servers.net. 21255 IN A 192.41.162.30
;; Query time: 399 msec
;; WHEN: Fri Oct 12 16:49:41 2012
;; MSG SIZE rcvd: 510
#################################################
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