I don't believe groups.io has anything misconfigured on their end, so I'm not sending this as a "bug" or support issue.? Mostly I'm putting it here to help other moderators/owners in case you've dealt with this, and to give some advice for remedy.
I have one group member who was unable to receive any groups.io emails.? Groups.io was showing the following error for all email deliveries to that one user:??us-smtp-inbound-1.mimecast.com: 554 Host network not allowed -?
In this case, their company uses a service called Mimecast as their company inbound anti-spam/anti-virus email gateway. From the error I was able to determine this is a result of them having implemented the geographic blocking functions of Mimecast to block emails from outside the US. Here's the interesting thing:? I also use Mimecast for my company email gateway, but I do not implement geographic blocking.??I tracked groups.io emails coming into my organization, and they all came from a single IP that, when I perform my own geo lookup, is identified as coming from California.?However when their IT group researched the blocked emails, they?determined that Mimecast was identifying the source IP for the groups.io emails as originating from Hong Kong.??
In this case, the "fix" is entirely on the receiving organization (they did implement a permit rule so the groups.io mail server IP was whitelisted), but you should be aware that this kind of blocking can occur from time to time, and is not explicitly something that groups.io can do anything about... but as a moderator/owner, you have the ability from the email delivery history for a user to get this kind of information to help your members diagnose why some emails may not be delivered.
For reference, the IP identified as the source for groups.io emails in my tracking is?66.175.222.12
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Bryan Jones
Kenwood-Hybrids group co-owner/moderator
TECSYS EliteSeries user group owner/moderator
