Sender verify callout

Using sender verify callout, Exim will attempt to contact the domain's DNS server to verify that the domain exists and is accepting email. If the DNS server cannot be contacted or does not return a valid response, the email will be rejected.

There are a few reasons why sender verify callout is a popular practice.

• First, it helps to protect against spam. Spammers often use fake email addresses to send their messages. By verifying the existence of the domain, Exim can help to prevent these messages from being delivered.
  
  
• Second, sender verify callout helps to protect against phishing attacks. Phishing attacks are emails that are sent to trick recipients into revealing personal information, such as their passwords or credit card numbers. By verifying the existence of the domain, Exim can help to prevent these emails from being delivered.
  
  
• Third, sender verify callout can help to improve email deliverability. Some email providers, such as Gmail, will reject emails that do not pass sender verification. By enabling sender verify callout, you can help to ensure that your emails are delivered to the intended recipients.

The "Sender Verify Callout not completed" error means that Exim was unable to verify the existence of the email sender's domain. This can happen for a number of reasons, including:

• • • The domain does not exist.
    • The domain's MX record is not pointing to a valid mail server.
    • The mail server is not accepting inbound email.
    • There is a firewall blocking the callout from Exim.

If you are receiving Sender verify Callout error,

• the first thing you should do is check the domain's DNS records to make sure they are correct. You can use a tool like WhatsMyDNS.net: https://www.whatsmydns.net/ to do this.
  
  
• If the DNS records are correct, then you should check the mail server to make sure it is accepting inbound email. You can do this by sending a test email to the server from another account.
  
  
• If the mail server is not accepting inbound email, you will need to contact the server administrator to troubleshoot the issue.
  
  

If you have ruled out all of the above possibilities, then the problem may be with Exim's configuration. Please raise a ticket so that we can investigate the issue.

Drawbacks to enabling sender verify callout.

• First, it can slow down email delivery. Each time Exim receives an email, it must make a DNS lookup to verify the domain. This can add a few milliseconds to the delivery time.
  
  
• Second, sender verify callout can be blocked by firewalls. Some firewalls are configured to block outbound DNS lookups. If your firewall is blocking outbound DNS lookups, you will need to configure it to allow Exim to make these lookups.

Overall, the benefits of enabling sender verify callout outweigh the drawbacks.

If you are concerned about spam, phishing, or email deliverability, we recommend

The best course of action is to work with the email sender to resolve the issue. This may involve making changes to their DNS records, their mail server configuration, or Exim's configuration.

As a last resort, If you are unable to resolve the issue, you can contact us to other secure paid options that will allow delivery of such emails.