Managed DNS Express: Fast, reliable DNS without breaking the bank. Get your first month FREE today! Get it now

Your Current Language Is:

Why can’t I send mail


Email delivery problems can often be difficult to troubleshoot, as there are many points along the way where a message could be delayed, rejected, or even silently dropped without the sender ever knowing a problem occurred. Your Email server or Client logs should show what error is occurring; if not, you can contact our support team for further help and make sure to include the full headers of any delayed or rejected Emails (including timestamps and Received: entries) where available, and describe the timeframe of the problem to the nearest hour with timezone.

If you did go over quota, you can add additional relay blocks, or wait for your quota to be reset the following day.

  • Make sure your Email client, or server, is configured to use the following settings:
    Outgoing SMTP Server:
    SMTP Port: 25 (default), 2525, or 10025
    SMTPS (SSL/TLS): 465 (default) or 10465
    Username: Your Dyn Username
    Password: Your Dyn Password
    Authentication Type: Basic (“Auth”, “Login”, “Password”)
    Use SSL/Encryption: Yes (recommended)
  • If you use SPF records, make sure to add “” to your record. You can learn more here.

You may have to refer to your client or server’s manual to see where those settings are.

Errors Authenticating:

Please make sure you are using your username, not Email address, and password; the same ones you use on our system.

Seeing “451 Temporary Local Error” or Sender Verify Failed errors?

These errors usually indicate a problem with your sending address. The most common causes are:

  • Typo in the sending domain ( instead of
  • Domain’s DNS is misconfigured (no A or MX record; MX record points to an IP address or CNAME; SERVFAIL)
  • Domain has expired or is unregistered (user@domain.local)
  • You have not waited fifteen minutes after purchasing the service for it to activate
  • Double-check your spelling and ensure your domain is resolving properly. A simple typo is almost always the culprit.

What is a relay? How are relays counted?

A relay is a single outgoing message sent through Dyn Standard SMTP. For messages under 10MB, each message counts for one relay. For example, if you send an email to ten people, you use up ten relays. Please see the chart below for messages over 10MB.

Dyn Standard SMTP can send messages up to 50MB in size. Messages larger than 10MB count for multiple relays, as described in the following chart

Message Size Multiplier
10MB – <20MB 2
20MB – <30MB 3
30MB – <40MB 4
40MB – <50MB 5
Exactly 50MB 6

Community Forum

Need help setting up your network? Ask your question in our community of networking experts.
Dyn Community Forum »

Email Support

Email support is available for all paid accounts, and is our preferred method of contact. If you have a paid service, please login to view the support page.

Phone Support

Phone Support is only available to customers with certain services. If you have a paid service, please login to view the support page.