SNMP and sending localhost mails

To just run a local catch all server:

docker run --rm -p 1025:1025 -p 8025:8025 mailhog/mailhog

to send an email

brew install swaks

# with default test subject and body
swaks --server localhost --port 1025 \
  --to saramic@gmail.com

these can be viewd in the mailhog browser view

open http://0.0.0.0:8025

To send real email, you would need something like a postfix relay? in the example below you could optionally limit to a set of sender domains with

` -e ALLOWED_SENDER_DOMAINS=”" \`

docker run -d \
  --name postfix-relay \
  -p 2525:25 \
  -e POSTFIX_myhostname="mail.milander.net" \
  -e POSTFIX_smtp_helo_name="mail.milander.net" \
  -e POSTFIX_mynetworks="127.0.0.0/8,172.16.0.0/12,192.168.0.0/16,10.0.0.0/8" \
  -e POSTFIX_smtpd_relay_restrictions="permit_mynetworks,reject_unauth_destination" \
  -e ALLOW_EMPTY_SENDER_DOMAINS=1 \
  boky/postfix

# at the end to remove the docker container
docker rm -f postfix-relay

now to send an email you can use the same swaks command or add a custom header and body as below and even add some From: headers to change who the email looks like it is coming from.

swaks \
  --to <SOME_REAL@EMAIL.COM> \
  --from <THE_REAL@FROM_EMAIL> \
  --header 'From: "YOUR FAKE NAME" < <YOUR_FAKE@EMAIL.COM> >' \
  --header 'Subject: THE SUBJCET' \
  --body 'THE BODY' \
  --server localhost --port 2525

looking at the server you can look at the logs

docker logs -f postfix-relay

where a successfull send would look like this, in this case using a fake FROM_FAKE_EMAIL@ADDRESS.COM and sending it to a REAL_EMAIL@ADDRESS.COM on mx1.dreamhost.com

2026-03-01T08:24:13.814711+00:00 INFO
    postfix/qmgr[994]: C61FB452021: from=< <FROM_FAKE_EMAIL@ADDRESS.COM> >,
    size=544, nrcpt=1 (queue active)
2026-03-01T08:24:13.815065+00:00 INFO
    postfix/smtpd[1398]: disconnect from unknown[172.17.0.1] ehlo=1 mail=1
    rcpt=1 data=1 quit=1 commands=5
2026-03-01T08:24:18.279605+00:00 INFO
    postfix/smtp[1402]: C61FB452021: to=< <REAL_EMAIL@ADDRESS.COM> >,
    relay=mx1.dreamhost.com[64.90.62.163]:25, delay=4.5,
    delays=0.03/0/3.8/0.65, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as
    4fNw8K693Wz7PJ9)
2026-03-01T08:24:18.280615+00:00 INFO
    postfix/qmgr[994]: C61FB452021: removed

and if the upstream mail server rejcets you, in this case as your residentiall IP address is on the spamhaus.org list of blocked IP addresses, it may look like this

2026-03-01T08:23:45.993782+00:00 INFO
    postfix/qmgr[994]: F0DAD452021: from=< <FROM_EMAIL@ADDRESS.COM> >, size=586,
    nrcpt=1 (queue active)
2026-03-01T08:23:46.797353+00:00
    INFO postfix/smtp[1402]: F0DAD452021: to=< <TO_EMAIL@ADDRESS.COM> >, relay=
    <UPSTREAM_RELAY AND IP >, delay=0.91, delays=0.11/0.02/0.73/0.06,
    dsn=5.7.1, status=bounced (host <UPSTREAM_RELAY AND IP > said: 550 5.7.1
    Service unavailable, Client host [ <SENDING_IP_ADDRESS> ] blocked using
    Spamhaus. To request removal from this list see
    https://www.spamhaus.org/query/ip/<SENDING_IP_ADDRESS> AS(1450)
    [ML1PEPF0001130A.ausprd01.prod.outlook.com 2026-03-01T08:23:46.760Z
    08DE7566F2DB722E] (in reply to RCPT TO command))
2026-03-01T08:23:46.823713+00:00 INFO
    postfix/bounce[1403]: F0DAD452021: sender non-delivery notification:
    C8D02452025
2026-03-01T08:23:46.823900+00:00 INFO
    postfix/qmgr[994]: F0DAD452021: removed

To manually connect and send an email you can

telnet localhost 2525

EHLO test
MAIL FROM:<VALID_FROM@ADDRESS.COM>
RCPT TO:<VALID_TO@ADDRESS.COM>
DATA
Subject: test

Hello world
.
QUIT

Other protection mechanisms include

  • IP reputation (historical behavior)
  • Domain reputation
  • SPF alignment
  • DKIM signature validity
  • DMARC alignment
  • Reverse DNS
  • HELO consistency
  • TLS usage
  • Sending volume patterns
  • User engagement (opens, deletes, spam clicks)
  • Content signals
  • URL reputation
  • Behavioral patterns