Email deliverability: How to solve a delivery problem?

Who hasn't found themselves at an impasse due to a delivery problem? Whether it's an IP/domain block from an ISP, a blacklisted IP/domain listing, a technical configuration problem... we've got you covered. every email deliverability problem has its solution !

Identify the problem

Reputation vs. technique

When you have a delivery problem, it is important to know the cause of the problem. This can be due to a reputation problem (bad targeting, high complaint rate, ...) or to a technical problem (bad IP/domain configuration, SPF signature failure, ...). In any case, you just have to look in your campaign statistics if one of the following four indicators is impacted:

  • Deliverability rate : a low deliverability rate indicates a block on one (or more) ISPs or a problem with your targeting (cf. high hardbounces rate). If you are not sure what the problem is, you can always check the bounces and see what type of problem it is (blocking vs. targeting).
  • Opening rates : A lower than normal open rate means that your emails were most likely delivered as spam (unless you targeted your bottom drawers).
  • Softbounces / Anti-spam filters : To get a clear idea of the problem, the smtp return codes returned by ISPs/MSPs can give you the meaning of a block (e.g. 421 mwinf5c30 ME Service refuses. Please try later. Service refused, please try later. OFR_999 (999) - in this case an Orange block of at least 2 hours).
  • Rate / Number of complaints : This indicator is very revealing of an ISP/Webmails blocking. If you exceed 1% with French ISPs (monitor your Signal-Spam complaints if your router is subscribed) and 0.3% with US Webmails (monitor your feedback loop or the Google Postmaster Tool interface), you are almost certain to have a delivery problem (more or less impactful).
    Logically, routers display a report by ISP/MSP, it is very easy to see if the problem is isolated on one ISP/MSP or on several.

Case study of a reputation problem

This is certainly the most frequent case that an advertiser may encounter. Here are the 5 most frequent cases that you will find:

  • IP/domain blocking due to a high complaint rate.
  • IP/domain blocking due to too many errors generated on the remote server (full boxes, hardbounces for example).
  • IP/domain blocking following the targeting of Spamtraps addresses from a blacklist.
  • Reputation problem of a domain used in your message (for example, a third-party tracking link).
  • Problem with message content.

Case of a technical problem

The technical problem is less common and is mainly on the router side (the problem can also come from the advertiser's settings). Here are the 5 most frequent cases that you will find:

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  • Incorrect setting of the IP address (it has a configuration fault on its PTR record).
  • Incorrect setting of the sending domain (information in the WHOIS record is hidden).
  • The SPF authentication system is missing (SPF checking is widely used as a first level of filtering).
  • The sender address does not exist (it forgot to be created).
  • MTA server configuration problem (over-solicitation of the remote server leads to IP blocking).

A solution for every problem

The reputation problem:

It is not necessarily obvious when you have a reputation problem to know what to do. Should I change my IP address after being blocked? Should I stop sending to the ISP/MSP where I am blocked? A lot of questions come up without necessarily having the right answers... I will try my best to guide you in solving your problem!

I have a block on one (or more) ISP due to a high complaint rate, what should I do?

  1. Find the impacted ISP/Webmail(s)
  2. Find the reason for the blockage yourself with the different indicators available (if no indicator, the best is to contact the ISP/Webmail directly via its Abuse or Postmaster address).
  3. Take the necessary measures to ensure that the incident does not happen again (for example, in the case of "too broad" targeting, make a commitment to the ISP not to target this population in the future, as it is too sensitive).
  4. (Re-)Contact the ISP/Webmail and support your request for unblocking with the measures taken (be careful, a commitment must be kept because there will be no second chance!)

I have a block on one (or more) ISP due to too many errors, what can I do?

  1. Find the impacted ISP/Webmail(s)
  2. Find the reason for this very large number of errors by yourself with the different indicators available (your bounces - hard & soft).
  3. Take the necessary measures to ensure that the incident does not happen again (for example, set up workflows to clean up your database for addresses that generate a lot of soft bounces or set up a welcome program to qualify your addresses before including them in your mass mailings).
  4. Contact the ISP/Webmail supporting your request for unblocking with the measures taken (be careful, a commitment must be kept because there will be no second chance!).

I have a block at an anti-spam organization because I targeted their spamtraps addresses, what should I do?

  1. Find out which organization listed you and check the information directly on their site (impact date, reason, delisting condition).
  2. Find the campaign and then the segment that targeted spamtraps.
  3. Take the necessary measures to prevent the incident from happening again (blacklisting the segment or the inactive population of the segment - the latter is very risky, we will opt for blacklisting the segment for safety reasons).
  4. Contact the organization (if the release is not automatic) and support your request for release with the measures taken (be careful, a commitment must be kept because there will be no second chance!).
    => Feel free to check out my article entitled "xxx" for more information (wait until the article on spamtraps is published to add the link :p)

I have a block because my external (or internal) tracking link is listed on a major blacklist, what can I do?

  1. Find the impacted ISP/Webmail(s)
  2. Isolate all the links in your message and test them one by one to see which link is at fault.
  3. Change it for another tracking system (prefer a dedicated tracking on a dedicated domain than a semi-dedicated tracking on a shared domain or a shared tracking on a shared domain).
  4. Logically, your IPs / domains are not impacted by this type of blocking. If this is the case, there may be another problem elsewhere, so contact the ISP/Wbemail concerned.

I have a block due to a problem with the content of my message, what can I do?

  1. Find the impacted ISP/Webmail(s)
  2. Cut up and test your message in pieces to find out what irritates the spam filter.
  3. Make the necessary changes (and re-test that everything is ok) before routing your campaign.
  4. Logically, your IPs / domains are not impacted by this type of blocking. If this is the case, there may be another problem elsewhere, so contact the ISP/Wbemail concerned.

The technical problem:

This part is more about your router (unless you use a dedicated infrastructure to send emails). It happens sometimes (much more now than in the past) that a blocking is due to a technical problem (I have experienced some more or less impacting ones in my previous experiences)

I have a block due to a wrong setting of my IP address, what can I do?

  1. Alert your host (or router) of the problem (especially if it has not noticed) (it will validate if the problem is real or not).
  2. Pause the campaigns (especially if you have only one IP) while the incident is resolved.
  3. After confirming the resolution of the incident, make a proofreading to validate the good reception of the message before resuming your mass or transactional sendings.

I have a block due to a wrong setting of the sender domain (hidden WHOIS information), what can I do?

  1. Pause all campaigns.
  2. Contact your network administrator (or web host) to change the domain's WHOIS information.
  3. After confirmation of the modification, make a proofreading to validate the good reception of the message before resuming your mass or transactional sendings.

I have a blocking problem due to the lack of SPF settings on my domain (or sub-domain), what should I do?

  1. Pause all campaigns.
  2. Contact your network administrator (or web host) to have SPF added to your domain.
  3. After confirmation of the addition, make a proofreading to validate the good reception of the message before resuming your mass or transactional sendings.

I have a block because of my non-existent sender address, what can I do?

  1. Pause all campaigns.
  2. Contact your network administrator (or web host) so that he/she can physically create the e-mail address on your domain.
  3. After confirming the creation of the address, make a proofreading to validate the good reception of the message before resuming your mass or transactional sendings.

I have a blocking problem due to a problem with the MTA server settings (it indicates that too many emails are being sent), what can I do?

  1. Pause all campaigns (there's no point in continuing to send if you're blocked :p).
  2. Alert your router of the problem in order to see if it has a configuration problem on its MTA servers (sudden modification of the configuration file).
  3. After confirmation from the router, restart the campaigns, watching the softbounces to make sure you don't oversubscribe the ISP/Webmail mail server again.

Conclusion

Nobody is perfect and especially nobody is safe from having, one day, a problem with an ISP. You have at your disposal all the tools you need to waste as little time as possible and to be efficient in solving the problem as soon as possible.

To conclude, take note that YOUR commitment will be essential to obtain an unblocking (there is nothing without anything). You should also know that the ISP/Webmail is not obliged to unblock you (especially if you have caused a major incident), so it is up to you to be very convincing in your approach!

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One Response

  1. Hello,
    What happens to mail blocked by mailjet due to incorrect settings.
    Once everything is ok, all the old blocked mails are delivered or are lost forever?

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