This error message indicates a delivery issue with your email to a Yahoo mailbox.
This is the mail system at host fx403.security-mail.net.
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# THIS IS A WARNING ONLY. YOU DO NOT NEED TO RESEND YOUR MESSAGE. #
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Your message could not be delivered for more than 0 hour(s).
It will be retried until it is 7 day(s) old.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report.
You can delete your own text from the attached returned message.
The mail system :
host mx-eu.mail.am0.yahoodns.net[*********] said:
421 4.7.0 [TSS04] Messages from ********* temporarily deferred due to unexpected volume or user complaints - 4.16.55.1; see https://postmaster.yahooinc.com/error-codes
(in reply to MAIL FROM command)
Here is an explanation of the code:
421: This is the general error code indicating a temporary delivery issue.
4.7.0: This sub-code specifies the reason: “Service available” with a temporary malfunction.
[TSS04]: This internal Yahoo code may not be publicly documented.
Messages from (Secuserve IP range): This is the IP address of the sending mail server, ours.
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temporarily deferred due to unexpected volume or user complaints: This is the key part. It means your email delivery has been delayed for one of the following reasons:
Unexpected volume: You may be sending a large number of emails within a short period of time, triggering Yahoo’s anti-spam protections.
User complaints: Some Yahoo users may have marked previous emails from the same IP address (85.31.212.35) as spam.
Here is what you can do:
Wait and retry:
This is a temporary issue, so your mail server should automatically retry delivery after some time.Reduce email volume:
If you are sending a high volume of emails, consider spacing them out over a longer period.Check the email content:
Make sure your emails are relevant and do not resemble spam in order to avoid user complaints.Check sender reputation:
Use online tools such as Sender Score or Cisco Talos to verify the reputation of your IP address regarding spam activity.Contact Yahoo Postmaster:
If the issue persists, refer to the link provided in the error message:
https://postmaster.yahooinc.com/error-codes
for additional resources and possible contact options with Yahoo Mail support (although contacting them directly may be difficult).Consider another email provider:
If you frequently send bulk emails, consider using providers specialized in mass mailing services, as they may offer better deliverability toward Yahoo mailboxes.