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+======Sender Domain Must Resolve======
+If you receive an 'SMTP Client Error' something like:
+''451 (user@domain.com) Sender Domain Must Resolve''
+this means that the ISP's mail server cannot find the domain.com part of the email address.
+Often this means that the FROM address of the message is invalid, or that the ''Settings -> Local Mail -> Default Domain'' is incorrect. This setting should always be a valid Internet email domain.
+Occasionally this can happen if you have just registered a new domain (or moved the domain to a new ISP) as the DNS entries for the domain can take a while to propagate to all DNS servers, so the mail server may be talking to a DNS server which doesn't recognise the name yet - in this case waiting a few hours may cause the problem to rectify itself automatically.
+If you know that the FROM addresses you are using are correct, try contacting the ISP to get them to check their settings - it is not unknown for their servers to be set up incorrectly.
+{{tag>SMTP client error_code domain resolve send}}

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