Intermittent email bounces


New Email
I am having a problem with emails from my account ( periodically bouncing when I send email addressed to people in one particular domain. Some emails will get through, but some emails to the same user will bounce back to me with the following error (different users at times, but same error in all emails):

Remote host said: 550 5.1.0 error: R4.1: [MAIL_FROM]

I can send you the full bounced email content if that is of additional use.

On the receiving side they checked with their ISP who reported the following ...

"We have checked the mail logs for the header information provided by you. The problem is that the IP the mail is coming from is not a valid MX for the domain, nor is the reverse in the same domain and the from address. One or the other has to be true for us to accept mail. Sender mail server has to be one of the mx records (if they have no control of reverse). Please contact the sender mail server admin to correct this."

Please help me to resolve this issue.



EQ Forum Admin
Staff member
Hi Randal,

The receiving ISP is running a broken mail service.

Yahoo provides the email service for

The reverse DNS identifies itself as Yahoo (and has a proper matching forward record):



The DNS does not have an SPF policy. It does not state that mail should not be accepted from them via the Yahoo mail servers.

If the receiving ISP is not going to accept the email from Yahoo mail servers for From:

  1. The person you are trying to reach should point out the problem their mail provider (again).
  2. If the receiving ISP says that they can not fix the problem then your contact should ask to have their ticket escalated.
  3. If the receiving ISP still refuses to fix the problem, the person you are trying to reach should find a new mail provider.
Please feel free to share the link to this information with the receiving ISP.

:welcome: to Email Questions!


New Email
Thanks for the quick response. I've sent your information to my business partner and they updated the ticket with their ISP and are waiting to hear back.