550 that SMTP username's account is not allowed to send
Also applies to: 550 that IP address is not allowed to send
This email rejection is generated if you have not yet verified your sending domain, or if you've added a domain name that was only recently registered.
If you haven't yet added and verified your sending domain, go to the "Settings > Verified Senders > Sender Domains" section of your dashboard.
Next, update your DNS entries to match those shown in your dashboard. A range of detailed DNS setup guides for common providers can be found here.
Once the DNS records have been updated, return to your SMTP2GO dashboard and click "Verify".
Once verified, sending will be enabled for your account.
If you have further questions regarding this or need assistance then please contact our support team anytime via email ticket, live chat or phone.