How to set up SMTP outbound relay service?  How to set up SMTP outbound relay service?

Our outbound SMTP relay service allows you to send emails through our servers, running both on standard (port 25) and non-standard ports (port 26, 2525, 465, 587).

Step 1: Sign up for SMTP outbound relay service

You may click here to sign up for SMTP outbound relay service for your domain name.

SMTP outbound relay

Step 2: Obtain SMTP relay host and login

After signing up for the service, you will be provided with our relay server host and your username and password to log onto this server to send out emails. You may do the following to set up your email server or client:

1. Use relay.dynu.com as outgoing SMTP server
2. Enable 'Outgoing SMTP server requires authentication'
3. Use the login username and password

If your ISP blocks outbound SMTP port 25, you may use port 2525, 26, 587 or 465 instead.

Step 3: Set up SPF record

You need to include the following string to SPF record for for relay.yourdomain.com:

a:relay.dynu.com

For example, your SPF record may look like v=spf1 a:relay.dynu.com ~all. You may use our SPF record generator to generate your SPF record. If your domain name DNS is managed by us, you may refer to this tutorial to set it up.

Step 4: Set up DKIM keys

There are two parts of DKIM keys, the public key that goes to the DNS record of your domain name and the private key that goes to our email server. Both keys can be generated using our DKIM wizard.

Use relay.yourdomain.com as 'Domain Name', mail as 'DomainKey Selector' and the key size should be 2048.

SMTP outbound relay


You will be asked to add a TXT record for mail._domainkey.relay.yourdomain.com.

SMTP outbound relay


If your domain DNS is hosted with us, you may add the record in 'DNS records' section: Use mail._domainkey.relay as 'Node', Type is 'TXT', and TTL can be set to any value from 90 to 1440. Copy the public key record to the 'Text' section as pictured.

SMTP outbound relay


You may verify that the TXT record has been set up correctly using the DNS lookup tool. Use mail._domainkey.relay.redtomato.click as 'Host' and the type is TXT. It may take up to 5 minutes to go into effect.

SMTP outbound relay


Now go to SMTP relay service setting for your domain name in the control panel. The private key will be set in 'DKIM Signing' section.

SMTP outbound relay


'DKIM Selector' is mail, Header Method' and 'Body Method' should be relaxed and the 'Signing Algorithm' should be SHA256. Copy the private key generated using the DKIM wizard to the 'DKIM private key' section.

SMTP outbound relay


You can test SPF and DKIM sigature by sending an email from user@yourdomain.com to a Gmail address. You should be able to see that DKIM and SPF pass in viewing the original email.

SMTP outbound relay