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Constant Contact Email Authentication


Constant Contact has an option called “Authentication” that you can turn on  (or off, if desired) directly from within your account. A lot of people might have heard the term authentication, but maybe not know how it can help them with their Constant Contact accounts. 


Definition: Email Authentication is a way to verify that an email is actually coming from the sender it claims to be coming from and for good emailing practices to be electronically tracked. It can help defeat email scams that involve spoofing, allow senders to be recognized in the industry as reputable email marketers and has several other benefits.


By turning this option on in your account, you clarify to receiving ISPs (Internet Service Providers) that you have authorized our servers to send these emails.  What does this mean in return? It means that your emails will have a higher chance of being delivered to your customers in boxes and not into a spam/junk folder, and have less of a chance of being bounced back by the ISP.


Some things to know before turning Authentication on:

  • The sender header address does not take the place of your "from" address, and will not affect your status on Safe Sender lists.
  • There is NO change to the look of your unopened email in the inbox.
  • Some email clients choose to make the address in the Sender header visible when the email is opened.
  • The sender header address may appear differently depending on the email client.
  • We create a registered sub-domain of in which your unique authentication credentials are published. ( is a domain used by Constant Contact to manage our customers' authentication credentials.)


To turn Constant Contact Authentication on:

  1. Click on the profile head, then select “My Settings” from the drop down.
  2. Click “off  next to “Authentication” in the box labeled “other” on the right side of the “My Settings” page. This will prompt you to create your sender header address. (Note: This address can be anything, but will always end with
    Authentication Box.png
  3. Click “Save”

Wondering what the person receiving the emails will see? Click here for an example!

If you run into any issues creating your authentication address, or just need more information, please click here to access our overview on Constant Contact Email Authentication!


I started with Constant Contact back in October of 2006, have wore many different hats with the company, gaining knowledge in a variety of Constant Contact departments.

Honored Contributor

Hi Ken,


Do you have a list of the ISPs that currently support this?



CTCT Employee

Hi Tony.


I understand you spoke with Ros. I hope that helped out!  

Honored Contributor

Good to go thank you.  



Occasional Participant

I signed up with Constant Contact a few days ago. I sent my first newsletter and my open rates were beautiful. Shortly after, I imported some of my older contacts that I have not used since January and had a few bounces. Ever since this point, my open rates (even with the original recipients) have dwindled severely. I added some test email addresses and it appears that my authorization server "" is automatically being detected as spam. Is there a way that my authorization server can be changed please? My list has since been cleaned and all bounces removed. 


Hello @FredG21. I'm sorry that your address is being detected by spam. We have a department that specializes in deliverability and would be best to speak to regarding questions on authentication and how best to use it. Here is a link for their phone numbers and hours of operation. 


Hi All,

User under my account are unable to send email this is the error message "We could not verify your authenticated Sender Address".

when I send a test email from my account the message show " the email is sent successful" but i am not getting the test email in my email ID"

Please advice on this



Sunny Batra

CTCT Employee

Hello @sunnyb,


Since this looks like an authentication issue, I'd recommend reaching out to our Deliverability / Account Review team. You can find their contact information and hours of operation here.