[There are numerous similar questions on ServerFault but I couldn't find one that was exactly on point]

Background: I use Gmail for my email client. My email is example@gmail.com. However the email that people communicate to me with is me@example.com. I run the server that hosts www.example.com and other domains, at ServerBeach.

Up to yesterday, I had SENDMAIL painlessly just forward emails to me@example.com to example@gmail.com and everything was fine, for several years in fact.

Suddenly my email stopped working - that is, my gmail account stopped receiving emails via the forward from my server.

Looking into it I found a bunch of emails sitting on my server with content like this:

... while talking to gmail-smtp-in.l.google.com.:
>>> RCPT To:<pitosalas@gmail.com>
<<< 450-4.2.1 The user you are trying to contact is receiving mail at a rate that
<<< 450-4.2.1 prevents additional messages from being delivered. Please resend your
<<< 450-4.2.1 message at a later time. If the user is able to receive mail at that
<<< 450-4.2.1 time, your message will be delivered. For more information, please
<<< 450 4.2.1 visit xxxxxx://mail.google.com/support/bin/answer.py?answer=6592 u15si37138086qco.76
pitosalas@gmail.com... Deferred: 450-4.2.1 The user you are trying to contact is
receiving mail at a rate that
>>> DATA
<<< 550-5.7.1 [ 1] Our system has detected an unusual rate of
<<< 550-5.7.1 unsolicited mail originating from your IP address. To protect our
<<< 550-5.7.1 users from spam, mail sent from your IP address has been blocked.
<<< 550-5.7.1 Please visit xxxxx://www.google.com/mail/help/bulk_mail.html to review
<<< 550 5.7.1 our Bulk Email Senders Guidelines. u15si37138086qco.76
554 5.0.0 Service unavailable
... while talking to alt1.gmail-smtp-in.l.google.com.:

From what I've been researching, I think somehow someone has/is hijacking my domain name or something and this somehow has caused gmail's servers to notice and cut me off. But I don't know really what's going on nor do I see whatever emails might be involved.

I've read stuff on zoneedit.com that sounds like they might have a solution in their service for what I am trying to do. I also read a lot about admining DNS and SENDMAIL and tried various things, but nothing works.

  1. Can you tell from my description what is going on that caused GMail's server to stop accepting email from my server and is there a way to stop it?
  2. What is the 'correct' way to configure things so that emails to me@example.com behave as if they were sent to example@gmail.com?
  • Haved you examined the log files for your mail server. How many messages was sent recently? Does that number look unusually high? – Zoredache Jan 6 '11 at 23:07
  • I just saw the "unusual rate of unsolicited mail" message today, but it looks like Google changed the code for it to 421-4.7.0. I hope this helps someone Googling about the problem. – David Grayson Nov 13 '14 at 0:16

On average, how many emails would you say are forwarded from your ServerBeach server to Google?

Do you have reverse DNS set up correctly with a matching "A" record for your ServerBeach Server? You can test that by doing an nslookup, but using your server's IP address for the query. I'm not sure how much you know about DNS so let me give you a brief overview:

  • An A record associates a domain name to an IP (so google.com's A record would be, for example.)
  • A Reverse DNS record does the opposite - so a query for would return "google.com" to continue the previous example.
  • Most of the time, rDNS is irrelevant. However, some mail servers (google for example) like to see a matching rDNS record as an indication that you're not a spammer. Having an incorrect or mismatching rDNS record could cause your mail to bounce.

Sending too many messages or misconfigured DNS could cause you to be tagged as a spammer.

Also, head over to CheckOR.com and test to see if your mail server is an "Open Relay," meaning that anyone can use your server to send email to whoever they want (That's bad - and spammers have tools to scan for open relays to use them to send their spam.)

| improve this answer | |
  • Ben, thanks... I am afraid I am in over my head here. In response to your post, I would expect no more than 100 emails to be forwarded daily from my server to serverbeach. ... And I didn't understand your answer regarding the reverse DNS. Note of course that the only DNS records I have the ability to change are the ones on my own server. Do you mean that I need an A record that points to google.com? .... Also regarding checkor.com, my server name is salas.com and as you can see, indeed there is a problem reported, but I have no idea how to deal with it. – pitosalas Jan 6 '11 at 23:23
  • Reverse DNS isn't your problem. Your MX server, s1.salas.com, resolves correctly in both directions. – blueben Jan 7 '11 at 0:04

I gave a presentation a couple months ago about reliable mail delivery, and avoiding blacklists. Hopefully it can help you.


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  • thanks. your presentation is over my head, definitely... Is there anyone out there who could give me a hand? – pitosalas Jan 7 '11 at 0:52
  • 2
    Unfortunately, mail delivery is a complex subject and no mail providers make it easy to discover why you have been blocked beyond the reasons they give. – blueben Jan 7 '11 at 1:28
  • 1
    @blueben, could you provide an alternative link? Perhaps a more permanent one to slideshare.net for example? – David d C e Freitas Nov 10 '11 at 13:03

I'm having the same issue but I use google apps. It seems any mail forwarded to google apps or gmail is failing. I think it to do with there new dkim signing of email. The forward doesn't work if the address doesn't match the cryptokey.

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I'm running a Postfix server and I encountered the same problem today. There are two issues to be aware of if you try to forward email from your server to a gmail account:

First, Google will reject some spammy messages at the SMTP connection time. If that happens, then your MTA might actually send a bounce message back to the (alleged) sender; this is known as backscatter and should be avoided. Additionally, the bounce message sent by your MTA might contain the name of the gmail account that it failed delivery to; this is not necessarily information that you want to be public. For reference, the SMTP message from Google looks like this:

550-5.7.1 Our system has detected that
550-5.7.1 this message is likely unsolicited mail.    To reduce the amount of spam
550-5.7.1 sent to Gmail, this message has been blocked. Please visit
550-5.7.1 http://support.google.com/mail/bin/answer.py?hl=en&answer=188131 for
550-5.7.1 more information. x47si18849303yhd.100 - gsmtp

Secondly, if this happens a lot, then Google might start rate-limiting the emails it allows your IP address to send, and you will get this message:

421-4.7.0 Our system has detected an unusual rate of
421-4.7.0 unsolicited mail originating from your IP address. To protect our
421-4.7.0 users from spam, mail sent from your IP address has been temporarily
421-4.7.0 rate limited. Please visit
421-4.7.0 http://www.google.com/mail/help/bulk_mail.html to review our Bulk
421 4.7.0 Email Senders Guidelines. u10si25718847yhf.138 - gsmtp

Unfortunately, it seems that these two issues combined make it impractical to forward email for yourself into your gmail account. I can't find any way to tell gmail "hey, this IP address is part of my mail-receiving system and you shouldn't mark it as a spammer just because it forwarded some spam to me".

Instead of forwarding to gmail, you should set up a POP3 inbox on your server and configure gmail to fetch mail from there.

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