SMTP Simple mail transfer protocol

SMTP / Email spoof tests

• https://emailspooftest.com/

• Basic server test 2023 - https://ssl-tools.net/mailservers

• Test mail - http://www.allaboutspam.com/email-server-test/ -> Send mail to "test @ allaboutspam.com"

• 2023-06 http://mail-server-test.online-domain-tools.com/

• Website check - https://www.amberloom.com/

• https://internet.nl/test-mail/

• 2023-06 send test email to server https://www.wormly.com/test-smtp-server/

• https://mxtoolbox.com/emailhealth

• 2023-06 apply to remove IP from https://www.spamrats.com/

Check / Removal spam lists

• 2023-06 Fixed https://spfbl.net/en/delist/ ==> check https://matrix.spfbl.net/103.252.118.112

• rbl.rbldns.ru

Verify smtp ssl/tls certificate

• printf 'quit\n' | openssl s_client -connect mail.example.com:25 -starttls smtp | openssl x509 -dates -noout
  
  printf 'quit\n' | openssl s_client -connect smtp.vigor.nz:25 -starttls smtp | openssl x509 -dates -text | grep "verify\|notAfter=\|vigor\|SAN\|DNS:\|Subject Alternative Name:"

Debug smtp sasl starttls authentication

• Connect and move to tls protected channel

  $ openssl s_client -starttls smtp -crlf -connect vigor.nz:25
  ehlo testconnection
  auth plain (base64encodedstring)

• test sasl (/etc/sasldb2 )with

  # sasldblistusers2
  # testsaslauthd -u user -p password -f /var/spool/postfix/var/run/saslauthd/mux

• add user to sasl

  saslpasswd -c -u mail.example.com -a smtpauth test

• view postfix smtp logs using journalctl

  journalctl -u postfix@-.service  -f

• Check tls certificate on smtp server

  # echo "quit" | openssl s_client -starttls smtp -crlf -connect <smtp.host>:25 | openssl x509 -noout -text | grep DNS:

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