You can use this online tool to test DomainKeys/DKIM/SPF. First of all, please open the online tool and click "Next Step" button to get a test email address. Secondly, send an email to this email address. Finally, a DKIM/DomainKeys/SPF report will be generated shortly.
Online DKIM Test Tool
Online DomainKeys Test Tool
Online SPF Test Tool
If you have a Gmail account, you can also send a test email to your Gmail email address. Open your email in Gmail web mail, and click "show details". If there is "signed-by: your domain", your DKIM signature is ok.
If you have a Yahoo account, you can also send an email to your Yahoo email address to test DKIM/DomainKeys signature. Open your email in Yahoo web mail, and click "Full Header". If there is "dkim=pass" in your email header, your DKIM signature is ok.
>> Using Selector
>> Using Sender Rule
Deploy Public Key in DNS server
Using Sender Rule
Appendix - Set up SPF record in DNS server
Appendix - Set up DMARC record
DKIM in IIS SMTP Service - Tutorial
DKIM in Exchange Server 2003/2000 - Tutorial
DKIM in Exchange Server 2007/2010/2013/2016 - Tutorial
Bulk Email Sender Guidelines