Unable to send email to an email address hosted by TOAST.net. Typically a bounced message is received with one of the following errors:
- 501 Domain must resolve.
- Delivery to the following recipients has been delayed.
- The following recipient's could not be reached: <email address> Could not deliver the message in the time limit specified. Please retry or contact your administrator.
- There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. Connecting IP must have valid PTR record for (sender's mail server IP)>
TOAST.net requires all servers delivering email to TOAST.net to have properly configured DNS. A reverse DNS lookup is performed on the server delivering email and if there is no reverse PTR name the email is rejected. To guard against spoofing, TOAST.net then does a forward lookup on the PTR name to make sure it matches the IP. If it returns a different IP the email has its spam rating is increased, which may lead to message rejection.
Example with correct DNS:
- Incoming mail connection from 184.108.40.206.
- Reverse lookup of 220.127.116.11 returns mail07.toast.net so the lookup continues.
- A forward lookup of mail07.toast.net returns an address of 18.104.22.168
- Since the original IP and forward lookup IP addresses match email is accepted.
- Forward this information onto your ISP or IT department to fix the DNS records.
- Make an A record pointing to your outgoing mail server.
- Make sure the above A record has a reverse PTR that is identical.
- The fix can be confirmed using MXToolBox's reverse DNS search tool.
To use MXToolBox to verify your DNS setup:
- Visit http://www.mxtoolbox.com/ReverseLookup.aspx
- Enter the IP address of your mail server.
- Click on the Reverse Lookup button.
- When corrected a PTR record will be displayed and messages from your system will pass the PTR record check that is used on many email servers.