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I have a client that I manage their IT systems for, including G Suite. About a month ago, several of their clients stopped receiving their emails. Some of these are clients they've been working with for months and others are brand new prospects that they're reaching out to for the first time. They don't receive any bounce back messages, the emails don't appear in the spam folder, and the reporting tools in G Suite show that the emails have been delivered successfully. I know that the reporting tools can only see so far into the emails delivery path, but it's what I've got for now. I've done anything and everything I can think of to solve this issue, but I'm out of ideas.

Other things to note are that they had a similar issue early in 2019 where their previous IT vendor set up Barracuda Essentials to use as a spam filter. They stopped using it back in July, though, and it cleared up the issue. When I on-boarded this client, I updated their SPF record (because it still included Barracuda in the record) and set up DKIM. Other than that, there had been no other recent changes to the DNS records or G Suite configuration before this issue started.

Things I've done/checked:

  1. Checked that SPF and DKIM records are correctly configured (Verified with G Suite support)
  2. Configured DMRAC and monitoring it with Mimecast's DMARC analyzer tool (We're at a ~99% alignment for both SPF and DKIM)
  3. G Suite support has verified that our domain reputation is in good standing
  4. The IP address for our website was blacklisted on 4 different lists, so we asked our host, GoDaddy, to move us to a new IP address. They did. (Although this shouldn't really affect our email as the website and email domain are totally separate and the website has no ability to send our receive email. Also the blacklists we were on stated that it could be because there are no MX records associated with the IP address, which there aren't)
  5. Sent test emails to other domains that we help manage. They were successfully sent and received (several of these email domains use third party spam filtering services or email security gateways but the emails were still received)
  6. Verified that our G Suite settings are correct and there aren't any weird routes, gateways, or anything like that, set up. (Verified with G Suite support)
  7. Set up a new domain within the same G Suite tenant and sent test emails emails. Their clients still don't receive them.
  8. Sent test emails without a signature. (The signature they use a a GIF of their logo)
  9. We had one of their clients whitelist us and they started receiving our emails. This could be a work around for existing clients but won't work for new clients they've never contacted before.

It seems like it's an issue with an overly aggressive spam filter on the receivers end, but it's too much of a coincidence that it started happening with multiple of their clients at the same time. Management also doesn't want us reaching back out to their clients IT teams as they say it would look bad on our part. So I can't contact them and see if the emails are being quarantined, which would explain why the users never sees the emails in their spam folder.

Any help or suggestions would be greatly appreciated.

Andrew A
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  • Have you tried a simple telnet session from their domain to the client? Telnet 25, HELO, MAIL FROM:, etc... ? The responses from the remote mail server may help you track this down. – Larryc Mar 26 '20 at 01:50
  • Also, it's my understanding that most mail servers do a reverse lookup and check MX records before accepting mail. – Larryc Mar 26 '20 at 02:04
  • Thanks for the suggestion Larry. I've tried sending some test emails by connecting to aspmx.l.google.com via telnet. Sending emails to my personal email works fine but sending it to email domains that aren't receiving emails give the error message "The email account that you tried to reach does not exist. Please try double-checking the recipient's email address for typos or unnecessary spaces." This occurs right after I enter the RCPT TO: command. I know for a fact that these emails exist and that the spelling is correct. – Andrew A Mar 27 '20 at 21:00
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    Well at least you know what the issue is,- the remote machine thinks the account doesn't exist. Assuming you typed the address manually then you can be certain its not spelling. How about this, setup a gmail account and send a message to those addresses from there, see if anything bounces. Other than that, convince management that you need to talk with just one of the clients tech support people. Whatever the solution turns out to be, it will likely be the solution for all of the failing client addresses.What ever the solution turns out to be, I'd like to hear about it. – Larryc Mar 28 '20 at 12:42

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