How Do Email Complaint Feedback Loops Work?

Posted: Tuesday, September 27, 2016
Posted by Ciara Noonan.


Many organizations spend thousands or even tens of thousands sending legitimate marketing emails every day. However, spam is in the eye of the beholder. A percentage of the people on any organization’s mailing lists may think of these marketing emails as spam.

It’s in the interest of marketers, email service providers (ESPs), and mailbox providers (MPs) to unsubscribe those users. Mailbox providers — the organizations that handle email delivery to users — and email service providers – for example, MailChimp – are highly sensitive to spam. MPs don’t want their users exposed to spam, and ESPs don’t want to end up on blacklists. Reliable email delivery is important for their business. 

What is a Feedback Loop (FBL)?

Feedback loops are one of the mechanisms by which the email industry attempts to make sure that users don’t receive email they … Read More »

Top SMTP Error Messages – June 2016

Posted: Friday, June 24, 2016
Posted by ksimpson.

In 2012, we posted a list of the world’s most popular SMTP response codes. We are now pleased to present an update to the list. Using a slightly updated script, we

Processed email delivery logs from the MailChannels Cloud SMTP relay service; Picked up all the SMTP response messages representing permanent delivery failures; Did a bit of string cleaning to remove serial numbers and other random-looking identifiers; and, Associated each log line with the organization that generated the error.

Here are the top rejection messages, organized by the network that generates the error:

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Response Code


GoDaddy (

550 5.1.0 23.83.x.y is not allowed to send from <> per it’s SPF Record. Please inspect your SPF settings, and try again. IB508  <>

The … Read More »

Why Outgoing Spam Filtering can and should be done transparently

Posted: Friday, April 29, 2016
Posted by ksimpson.

Spammers take root on customer machines, compromise email accounts and WordPress plugins, and use sophisticated techniques at obfuscating their identity in order secure hosting resources. Fortunately, it’s possible to filter outgoing email transparently using software. Done properly, transparent SMTP filtering is scalable, lawful, and effective.

Web hosting providers can find it challenging to ensure a clean IP reputation. Unfortunately, the internet itself is not free of misinformation about outgoing email filtering. In this blog post we challenge three suggested alternative methods for cleaning up your IP reputation:

Blocking port 25: Web hosting clients should not be restricted from using a port that is lawful to use (unless you’re spamming, of course). Most providers we talk to would not consider blocking port 25, for fear of losing customers. Still, this option is often promoted as a quick solution to the spam… Read More »

MailChannels launches Reseller partner program

Posted: Tuesday, March 15, 2016
Posted by dliao.

We know you want new, value-added services to bring to your hosting customers. And we know your team spends a lot of time resolving email issues. So we’ve designed a single, easy solution to meet those two challenges: the new MailChannels Reseller partner program.

Email is our sole focus at MailChannels. It’s important to us that we provide our customers with the best anti-abuse tools for your business. We’ve taken our carrier-grade on-premise software and extended it via MailChannels Cloud so that web hosting companies of all sizes can benefit from the same techniques.

This program provides our Reseller Partners with the tools, training, and resources needed to make it simple and profitable to offer email security products to your hosting customers.

MailChannels Reseller Partners are able to:

Provide exceptional email deliverability for their hosting customers Earn ongoing revenue from… Read More »

MailChannels Named Top Tech Company in Rocket Builders’ “Ready to Rocket” List

Posted: Thursday, March 03, 2016
Posted by dliao.

This week, the Vancouver-based consulting firm Rocket Builders released its 14th annual “Ready to Rocket” lists. The “Ready to Rocket” lists identify British Columbia technology companies that are positioned to grow quickly. We’re proud MailChannels landed a spot on the Information and Communications Technology (ICT) list.

This annual list is a predictor of privately-held tech companies that will likely experience significant growth, venture capital investment or acquisition in the coming year. MailChannels is growing fast – in the past year, we experienced explosive revenue growth, our headcount doubled and we secured a new brick and timber office in historic Gastown to accommodate our growing team.

“I’ve had the opportunity to interview most of the companies on our lists,” said Reg Nordman, Managing Partner at Rocket Builders, “The diversity of solutions, maturing skill sets of management and the resulting increased ability … Read More »

Tackling Greylisting in MailChannels Cloud

Posted: Thursday, December 10, 2015
Posted by ksimpson.

MailChannels Cloud sends enormous volumes of email through a large and complex infrastructure that spans the globe. But recently, we began encountering a serious challenge from a relatively old and yet still commonly used anti-spam technology called “greylisting”.

What is Greylisting?

According to Wikipedia, greylisting is an anti-spam technique in which the “mail transfer agent (MTA) … will ‘temporarily reject’ any email from a sender it does not recognize. If the mail is legitimate the originating server will try again after a delay, and if sufficient time has elapsed the email will be accepted.” Greylisting can be an effective defense against spam originating from simplistic botnet SMTP clients, which do not have an internal message delivery queue and cannot retry delivery if the first attempt fails (as it does when the receiving server is implementing greylisting). Legitimate email senders always … Read More »

Should I build my own mail server?

Posted: Tuesday, October 06, 2015
Posted by ksimpson.

With Edward Snowden’s revelations about government snooping into our private email, some technically-minded folks have considered setting up their own mail server in the hopes of staying clear of prying eyes. Is this a good idea? Probably not. And here’s why.

Setting up a secure email server takes a great deal of expertise and effort. You need to master a variety of protocols, from DKIM and SPF, to TLS. You also need to build a capable spam filtering system to protect yourself from email-borne offers and malware, and you need to contend with the nightmare of outbound delivery and IP blacklisting. When you’ve done all this, you also need to make sure the server is constantly kept up to date with the latest security patches, lest a global network of well funded state-level hackers gain access to your box to … Read More »

Spamhaus responds to SoftLayer’s Brazilian problem

Posted: Thursday, October 01, 2015
Posted by ksimpson.

Spamhaus, the world’s leading IP reputation advisory service, today released an analysis of an ongoing spamming issue at IBM’s SoftLayer web hosting subsidiary. According to Spamhaus, spammers have been targeting weak security measures at SoftLayer to obtain large numbers of IP addresses from which to send spam targeting Brazilian recipients. As a result of the spamming activity, Spamhaus has listed several hundred IP addresses owned by the provider under the common heading “Massive source of malware-distribution spam”.

Spammers routinely target web hosting providers like SoftLayer in an effort to obtain new resources from which to send spam campaigns. As Spamhaus and other IP reputation outfits block the offending IP addresses, spammers are hard at work exploiting any weaknesses in the provider’s security posture to obtain more. In the present situation, according to Spamhaus, the provider is not doing enough to … Read More »

STARTTLS Adoption Update

Posted: Thursday, October 01, 2015
Posted by ksimpson.

Updated October 1, 10:40am Pacific

In May 2013, Facebook published a detailed survey of TLS encryption usage by the world’s email servers. That survey indicated that about 37% of mail servers (as measured by IP address) did not at the time advertise the availability of TLS encryption for protecting the privacy of email sessions and data.

Fast forward to September, 2015 and the picture is improved, but not as much as we would have hoped. Analyzing email traffic sent to a diverse set of over 17,000 25,000 Internet email servers during a two hour twelve hour period on September 30, we found that TLS encryption is now advertised by 72% of mail servers (28% do not advertise it). This implies that the TLS encryption hold-outs have been reduced from 37% to 27% – an improvement of about a third in … Read More »

New ways to battle eavesdropping

Posted: Friday, September 11, 2015
Posted by dliao.

Unless you use end-to-end encryption such as PGP, the contents of your email message may be revealed to or even silently modified by sophisticated attackers with access to Internet backbone traffic. To prevent eavesdropping and modification, Internet engineers developed the Transport Layer Security (TLS) protocol, which email servers use to encrypt and protect email while it transits the Internet from server to server.

Edward Snowden’s revelations in 2013 about government snooping prompted large email providers such as Microsoft® and Yahoo! to implement TLS so that servers sending email to the servers can encrypt messages during transmission. After a lengthy period of implementation and testing, about 67% of mail servers in a broad survey now support TLS.

To ensure the privacy of our customers’ email messages, MailChannels Cloud now automatically encrypts connections to receiving mail servers that support the TLS … Read More »