Short version - verify your email with SES and configure your DNS correctly for SPF as described here: https://www.tendenci.com/help-files/tendenci-forms-email-notifications/ 

Association Management Software (AMS) frequently also serve as CRM systems and are used to email to contacts, members, and everyday notifications. It can be frustrating when your email doesn't get delivered. This is almost always a result of your DNS configuration.

We want you to succeed in your email sending! We realy do. But unlike other vendors email that goes out from a Tendenci site goes out under YOUR DOMAIN NAME. Therefore successful email sending can be a bit technical. Blame the folks that invented the Internet.

Helpful, but non-binding, advice on sending emails from Tendenci. Two scenarios - cloud or self hosted.

1) Emailing from your Tendenci Hosted site 

STEP 1 - Check your site settings to be SURE all email (no-reply, webmaster, admin, contact, etc) *all* end in your domain name. You can't send "webmaster-fictional-organization@gmail.com" for the domain "fictional-organization." This is logical as "example.org" is not the same domain "fictional-organization.org." Using the demo site as an example, your site settings are at 

Run a DNS report using https://www.dnsstuff.com/ 

STEP 2 - Fix your DNS

1. For example, mailgun will NEVER send email unless you follow their rules. Check Mailgun's support.
2. If you do not have an SPF record it will never send your email. Period. YOU must configure your DNS. In the screen shot below from dnsstuff - we have observed that most SMTP relay providers like mailchimp or mailgun will NOT send email due to this error.

• For help with mailchimp, mailgun, etc, please contact your email sender directly. 
• Example: https://www.mailgun.com/blog/how-to-deliver-email 

STEP 4 - If hosted on the Tendenci AMS cloud, but sure your have validated your email with the AWS SES validation email you should have received. If you did not, check your spam folder. If that fails contact Tendenci to request a new validation email. If you do not validate your email with AWS (our outbound gateway) your email will not get sent.

STEP 5 - Tendenci Cloud specific advice for mailgun. Again, please FIRST read your mailgun logs, contact mailgun, read their support files. This is not a Tendenci issue. Have your network administrator review these two help files perhaps before contacting mailgun.

https://www.tendenci.com/help-files/how-do-i-configure-my-mailgun-account/ 

https://www.tendenci.com/help-files/tendenci-forms-email-notifications/

Once you have read those help files - please verify your DNS configuration again at https://www.dnsstuff.com/ 

Then send another test email and talk directly to your email relay provider.

2) Sending from your self hosted Open Source AMS Tendenci site.

Almost all of the above applies similarly, except your spf record will be completely different. Google for "SPF TXT records" and go from there.

What if the above doesn't solve it?

Reread this SPF helpfile and dig into the details of the SPF RFC. This is not an easy task, and we recommend you contact your network technical support person as this is not an issue directly related to your web site.

Seriously - reread this in detail --> https://www.tendenci.com/help-files/tendenci-forms-email-notifications/ 

Finally - check the reputation of your sending IP address https://www.talosintelligence.com/reputation_center/lookup