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Fri, Jun 02, 2017 10:44 pm

Using nslookup to check an email blocklist

I was notified by someone today that yesterday he had sent an email to a mailing list on an email server I maintain, but the email had not been delivered to recipients. When I checked yesterday's email log, I didn't see any email from his email address, so I asked him to resend the message. He did so, but that email message was also not delivered and I didn't see any log entry for his email address in today's email log, /var/log/maillog. He has a verzion.net email address and Verizon recently transitioned its email service to AOL. I remembered helping him make that transition last month, so I looked for any aol.com entries in the log file and found the entry below for an attempt by an AOL email server to deliver a message that was rejected at the time he told me he had sent the email today.

# grep aol /var/log/maillog
Jun  2 10:50:16 moonpoint sendmail[23955]: ruleset=check_relay, arg1=omr-a006e.m
x.aol.com, arg2=127.0.0.6, relay=omr-a006e.mx.aol.com [204.29.186.55], reject=55
0 5.7.1 Spam Block:mail from 204.29.186.55 refused - see http://dnsbl.sorbs.net/

[ More Info ]

[/network/email/spam/sorbs] permanent link

Sun, Apr 30, 2017 8:33 pm

SORBS Blocking Email from Gmail

A family member reported that she hadn't received an email message sent to her today by a Gmail user who had sent her message in reply to the family member's email to her. Since I administer the Sendmail email server she uses, I checked the Sendmail log file at /var/log/maillog. I saw the outgoing email sent to the Gmail address, but no incoming email from that address. So I sent email messages from a Gmail account I have as well as email messages from other external addresses to the root account on the server. The other email messages arrived, but none I sent from the Gmail account arrived. So I ran tcpdump on the server to capture data to/from port 25 on the system, which is the well-known port for Simple Mail Transfer Protocol (SMTP) traffic. I then sent another email message to the root account on the Sendmail server from my Gmail account. After allowing several minutes for an attempted delivery from the Gmail server to occur, I stopped the packet capture with Ctrl-C.

# tcpdump -i enp1s4 port 25 -w smtp_2017-04-30.pcap
tcpdump: listening on enp1s4, link-type EN10MB (Ethernet), capture size 65535 bytes
^C225 packets captured
225 packets received by filter
0 packets dropped by kernel
# ls -lh smtp_2017-04-30.pcap 
-rw-r--r--. 1 tcpdump tcpdump 33K Apr 30 12:33 smtp_2017-04-30.pcap
#

[ More Info ]

[/network/email/spam/sorbs] permanent link

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