https://www.limilabs.com/blog/sign-emails-with-dkim
https://support.rackspace.com/how-to/create-a-dkim-txt-record/
http://www.mecatronica.eesc.usp.br/wiki/index.php/Verifiying_DKIM_signatures
http://dkim.org/specs/rfc4871-dkimbase.html
Quick reference to Internet message headers:
https://www.cs.tut.fi/~jkorpela/headers.html
HOWTO define DKIM/ADSP RRs
http://www.zytrax.com/books/dns/ch9/dkim.html#examples
Online Test Tool:
https://mxtoolbox.com/SuperTool.aspx
https://dmarc.org/resources/deployment-tools/
DMARC
https://dmarc.globalcyberalliance.org/
DMARC resource record in the DNS
"v=DMARC1;p=reject;pct=100 rua=mailto:postmaster@dmarcdomain.com"
| Tag Name | Purpose | Sample |
|---|---|---|
| v | Protocol version | v=DMARC1 |
| pct | Percentage of messages subjected to filtering | pct=20 |
| ruf | Reporting URI for forensic reports | ruf=mailto:authfail@example.com |
| rua | Reporting URI of aggregate reports | rua=mailto:aggrep@example.com |
| p | Policy for organizational domain | p=quarantine |
| sp | Policy for subdomains of the OD | sp=reject |
| adkim | Alignment mode for DKIM | adkim=s |
| aspf | Alignment mode for SPF | aspf=r |
Refer to
https://tools.ietf.org/html/rfc7489#page-16
Google, Microsoft, Yahoo
Troubleshooting
Gmail: https://support.google.com/a/answer/3726730?hl=en
Outlook.com: https://mail.live.com/mail/troubleshooting.aspx
Yahoo: https://help.yahoo.com/kb/mail/practices-senders-sln3435.html
AOL: http://postmaster.aol.com/Postmaster.Troubleshooting.php
https://www.mailenable.com/kb/content/article.asp?ID=ME020003