2019/10/07 by Jérôme Gays.

SFR Deliverability: Explaining error codes (GU_EIB) and the ongoing error threshold

Before getting to the actual matter, it is important to brush upon a few relevant chronological events in the past regarding SFR. Even though SFR has been carrying this name since 1987, the many other departments in this group have changed quite a lot ever since. During the past 10 years, SFR has made the acquisition of other Internet providers (or reincorporating branches) such as Neuf Telecom, Club Internet and so on.

This background will help us to gather the email domain names employing SFR’s infrastructure. Some of them well-known, some others not that much. Below, the list of the domain names performing SFR emailing service. Hence, the same spam filtering technologies:

@sfr.fr
@neuf.fr
@9online.fr
@9business.fr
@cegetel.net
@club-internet.fr
@cario.fr
@guideo.fr
@mageos.com
@fnac.net
@waika9.com

SFR’s Deliverability Error Code Explanation: GU_EIB_02 And GU_EIB_04

Using our experience and our deep analyze of the SMTP routing logs, Postmastery attempts to provide better SFR-based mailing deliverability thanks to its clear insight of the MTA process.

When your IP address is blocked, SFR’s bounces are sent, allowing you to find out the reason of your actual blocking. Below you will find the two examples we are concerned about:

• GU_EIB_02 : “5.7.1 <example.com[xxx.xxx.xxx.xxx]>: Client host rejected: Abus detecte GU_EIB_02”
• GU_EIB_04 : “5.7.1 <example.com[xxx.xxx.xxx.xxx]>: Client host rejected: Abus detecte GU_EIB_04”

WHICH ARE THE DIFFERENT SFR INDICATORS?

There are two major SFR-analyzed indicators. They will help at deciding when to block an IP address or not.

The fist one is the spam rate (GU_EIB_04). If a great deal of your mails is filtered as spam, it is likely that your IP addresses are blocked during a certain amount of time. It is worth to know that SFR, as well as Orange and Free, employs the French Vade Retro filtering technologies in order to sort legitimate email from spam.

The second indicator is the invalid email address rate generated by your sent emails (GU_EIB_02). This last one takes into account your data management quality. As we can confirm, maintaining a clean list is a key factor to profit from good deliverability.

FACING A THRESHOLD MATTER

Email rejecting is the result of high rates of invalid email addresses, as well as abnormal spam rates. In both scenarios, when 20 emails or more have been sent, SFR establishes the threshold at 25%. If we take hold to the idea that the invalid-address rate considered by the industry as valid (less than 3 or 4%) we realize that SFR-generated threshold will not aim clean-listed senders.

LENGTH

One must consider two kinds of length.

Sampling Window: It lasts for around 5 minutes. It means that if 25% of spam reporting or bounces is exceeded for more than 5 minutes, your emailing will be blocked temporarily.

Blocking duration: Once the threshold catastrophe is reached, your email sending will be blocked for about 20 minutes. However, if the emailing criteria are not complied, you will be blocked for
another 20 minutes, and so on. This may relevantly slow-down the speed of email sending.

BRIEFING THE TOPIC

GU_EIB_02

• Indicator: Invalid email-address rate
• Threshold: 25%
• Sampling Window: 5 minutes
• Blocking duration: 20 minutes

GU_EIB_04

• Indicator: Spam sorting
• Threshold: 25%
• Sampling window: 5 minutes
• Blocking duration: 20 minutes

Technical Implementation
In order to ensure proper management of this situations, it is imperative to employ a SMTP server enabling identification of this sort of feedback (GU_EIB_02 et GU_EIB_04 codes) simultaneously adapting itself in real time.

Unfortunately, Postfix, Qmail or Sendmail opensource servers do not empower built-in management facing this kind of behavior. With this in mind, Postmastery encourages our customers to actively employ PowerMTA. This last one enhances a backoff mode and connectivity management. If you want to learn more about PowerMTA, do not hesitate to contact us.

It Is Comments Time
ARE YOU AFFECTED BY GU_EIB_02 EVEN THOUGH YOU ARE CLEANING YOUR LISTS ON A REGULAR BASIS?
In this case, it is highly possible that you are not the sole person employing this blocked IP address. This is the case, for instance, of mails sent from your own web server. The only likely solution is to utilize an specific IP address or an specialized SMTP bridging. Please feel free to contact us if you want to implement personalized SMTP solutions.

WHAT ABOUT NUMERICABLE?

As you certainly know, Numericable has recently become a SFR acquisition. For now, deliverability has not been affected. Numericable remains to employ the same MX servers they did before. Postmastery will keep you informed about every update on this issue. If you have any further questions or need more information, please feel free to contact us.