Exim mail forwarding – Best practices to avoid IP blacklisting

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Mail forwarding is a boon to email users. It helps to collect all your emails at a single account.

Unfortunately, when you have setup too many email forwarders it can result in server IP blacklisting.

To avoid this, we need to configure Exim mail forwarding properly.

At `1 onlyhost , we often get requests from server owners to configure Exim mail servers as part of our Server Management Services.

Today, we’ll see the best practices that our Dedicated Engineers follow in Exim mail forwarding.



Mail forwarding and its affects

In simple words, email forwarding is the re-sending an email message received in one email address to another address. Literally, it just moves message to a new destination. Here, the forwarding server will not have much control in the mail path. It just transfers the mail as it is.

Then, what’s the effect of Exim mail forwarding in live mail servers?

Let’s check further on this.

For example, consider the scenario where a user forwards mail from his own domain to an external email address, say Gmail. Here, he will set a mail forwarder from user@domain.com to user@gmail.com.

And, the mail server will transfer each and every mail to the Gmail server. This will work fine, until spam comes into the picture. When there are no proper security systems, mail server will happily relay spam to gmail. This would cause gmail to think the spam is originating from your server. Considering the volume of mails, the server will get into the blacklist, even though the spam came from somewhere else. Additionally, the mail server will have a low reputation score too.

Luckily, to avoid all these hassles, our Support Engineers take extra care while configuring Exim email forwarding.


Tips in Exim email forwarding

From our experience in managing mail servers, we often get requests from customers regarding problems with mail forwarding.  Let’s see the top things that our Support Engineers do avoid forwarded emails tagged as Spam.


1. Disable catch-all emails

Firstly, we disable forwarding catch-all email accounts on the server. A catch-all email address is nothing but an account that receive mails for non existing email accounts. Usually, many users configure it as an external email address. This would cause too many emails forwarded from the server.

Here, our Dedicated Engineers set the default catch all account for all users in the server to “:fail:” As a result, server just reject the messages.


2. Enable Sender Rewriting Scheme (SRS) Support

Similarly, when one of our customers reported problems with Gmail marking mails as spam, we could see that too many mails were forwarded to Gmail. This eventually caused the server to lose its reputation. A solution for this problem is to enable Sender Rewriting Scheme (SRS).

The Sender Rewriting Scheme (SRS) rewrites the envelope sender address of an email message. Without enabling SRS, the forwarded mail will appear as if originated from your server rather than the the initial sender.  And, the situation becomes worse when there are lot of SPAM mails receiving to your domain’s email accounts and have Gmail forwarders too.

Therefore to fix the problem for the customer, we enabled SRS support in Exim configuration from WHM panel. The option look as shown in the picture.


3. Rate limit email forwarders

Yet another step to properly setup Exim mail forwarding include rate limiting the amount of emails forwarded from the server. In the server that we manage, we setup custom scripts to quantify the exact number of external emails originating from the server. And, we setup custom alerts to customers to notify about the email limit too.

[Need help in setting up Exim mail forwarding properly? We can help you.]



In a nut shell, following best practices in Exim mail forwarding greatly helps to avoid IP blacklisting. Today, we saw the steps that our Support Engineers follow in Exim to avoid forwarded mails tagged as spam.

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