Have Mailcow set up for several domains. Everything working nicely. I can connect my laptop via smtp and send emails to the world from all domains.
Now I have that web application on a cloud server. The server’s dns name belongs to one of my domains. There is a dedicated mailbox in this domain which works. The application sends out mail by authenticating with the credentials of that mailbox (using javax.mail…). Mail with a destination of a mailbox of any one of my domains gets through, but when I send mail to a 3rd party domain like hotmail.com or any such Mailcow accepts the connection but then complains:
MAIL FROM:<my-sender@my-domain.tld>
250 2.1.0 Ok
RCPT TO:<my-dummy@hotmail.com>
554 5.7.1 <my-dummy@hotmail.com>: Relay access denied
DEBUG SMTP: Invalid Addresses
DEBUG SMTP: my-dummy@hotmail.com
DEBUG SMTP: Sending failed because of invalid destination addresses
The sender my-sender@my-domain.tld exists and has the credentials my application uses.
What am I missing here?
THX a lot for any help