I was just informed by Mailgun support that it is not possible to configure the maximum number of messages sent per IP address per second to any specific IP address. My client is therefore unable to rely on the messages sent via their dedicated Mailgun IP address to their very own mail server, which is hosted by Tucows.

Also, it took me many months of submitting tickets, sending tests, and talking to Mailgun Support to trace this as the deliverability problem that I have been trying to resolve. This fact is not advertised anywhere that I can find and it was a hugely difficult process to finally discover that this is the root of the issue.

We may need to find a new mail host or sender host. It's a shame that two large corporations have policies that contradict each other. This makes it very hard to be your customer.

This is very frustrating.

I signed up for a free account in early January. I got an email from Sam saying to post feedback in here even if it is negative. So far overall it's a good service except for this problem. Initially I hesitated to complain about this because I have a free account but if I were to convert to a paid account this problem might inhibit me from doing so and instead find a different provider.

Here's the problem. I have some wordpress sites and I integrated mailgun as the smtp sender for either contact forms or registered site users. I created some routes which use both gmail and yahoo email addresses. Without fail every time the email to yahoo is dropped with this error message:

Retry limit reached. Dropped: postmaster@mydomain.com → user@yahoo.com 'Email from mydomain.com contact form' Server response: 421 4.7.0 [TSS04] Messages from 104.130.122.30 temporarily deferred due to user complaints - 4.16.55.1; see https://help.yahoo.com/kb/postmaster/SLN3434.html

I put in a ticket about this and the reply said that that the error means that "The error that you are seeing is ESP throttling, and this occurs whenever the recipient's email service provider (ESP) has received a large number of emails from a specific IP in a short amount of time. Due to this, they will not accept messages for a certain period of time (usually an hour) until they have processed all the emails from the original batch sent. ".

I googled the error and that is in fact the generic meaning of the error. However in this case yahoo specifically altered the error message to say: "temporarily deferred due to user complaints "

Over time emails to yahoo are never delivered due to this error. I don't believe the problem here is ESP throttling, it's due to a bad reputation on this ip address caused by a user presumably at mailgun which affects everyone using this shared ip address. I googled how to fix this and it seems that it's incredibly difficult to solve with yahoo and the owner of the ip address has to deal with it.

I hope that someone at Mailgun can look into this and fix it. Right now my sites don't generate enough money to pay for a dedicated ip. So if it can't be fixed I am going to have find another vendor. Thank you.

Reputation is everything in email delivery.

From your own documentation: "One of the most important assets you have in the email world (much like the real world) is your reputation. If you do not have a good reputation tied to your domain and your IP address (“IP” used herein for abbreviation), your email will not reach your recipients’ inboxes." (https://documentation.mailgun.com/best_practices.html#reputation)

It'd be nice to access the sender score [on a per domain basis] through the API. Knowing that info, directly, would give domain holders the warm fuzzies on their reputation without having to go elsewhere (senderscore.org).

Marco @ mailgun requested I write this here. Hi Marco! :) This is per support ticket #226672.