Friends
I spent more than a week trying to get email working on OpenProject Community Edition (installing on AWS instance). I finally resolved it in the following manner:
1. SUSE Linux Enterprise 12 instance
2. AWS SES Setup (followed process to obtain SMTP user credentials using AWS SES Console; https://docs.aws.amazon.com/ses/latest/DeveloperGuide/smtp-credentials.html)
3. OpenProject installation from: https://www.openproject.org/download-and-installation/#installation (RPM/Deb Packages; SUSE Linux Enterprise Edition 12 chosen as Linux Distribution)
4. Finally, the below key config parameters (username, passwords morphed; use what’s relevant in your case):
EMAIL_DELIVERY_METHOD=smtp
ENABLE_STARTTLS_AUTO=true
SMTP_AUTHENTICATION=login
SMTP_DOMAIN=bingo.com
SMTP_ENABLE_STARTTLS_AUTO=true
SMTP_HOST=email-smtp.us-east-1.amazonaws.com
SMTP_PASSWORD=Jimmys3SIP+JImmysda9dJwGtm0It4gpJIMMYvI/dJIM
SMTP_PORT=587
SMTP_URL=smtp://JINGCHAQM2YFLKIAJING:Jimmys3SIP%2JImmysda9dJwGtm0It4gpJIMMYvI%2dJIM@email-smtp.us-east-1.amazonaws.com:587/bingo.com
SMTP_USERNAME=JINGCHAQM2YFLKIAJING

Hope this helps & thanks to the OpenProject community!
Cheers!