Dear Dynu Support,

I am using your SMTP outbound relay service for the domain darko-mail.com, but emails sent via relay.dynu.com are not reaching recipients — neither in inbox nor spam folders, and no bounce messages are returned. My Synology MailPlus Server reports the status as “Sent”, but the messages are not delivered externally.

Here are the technical details of my setup:

• SMTP Host: relay.dynu.com
• SMTP Username: relay@relay.darko-mail.com
• SMTP Port: 587
• STARTTLS: Enabled
• Authentication: Enabled
• SPF record: v=spf1 include:relay.dynu.com ~all
• DKIM: Enabled and DNS record published
• DMARC: Configured with p=quarantine
• PTR record: Reverse DNS matches mail.darko-mail.com
• Mail server: Synology MailPlus Server (latest version)

I’ve tested delivery to multiple external addresses (Gmail, Outlook, Mail Tester), but none of the emails arrive. Mail Tester reports a score of 0/10, with the following error:

“You are not allowed to use one of your sending addresses”

This suggests that the SMTP relay does not authorize my sender address darko@darko-mail.com.

Could you please verify:

1. Whether the domain darko-mail.com is properly linked to my SMTP user relay@relay.darko-mail.com
2. If domain ownership needs to be verified or additional DNS records added
3. Whether any restrictions are preventing delivery from my address

I can provide email headers, logs, or test results if needed. Thank you in advance for your assistance.

Best regards,
Darko Vuoković
Zagreb, Croatia