I just want to share my experience with SparkPost support here because O am simply blown away by their service (I’m still on their free plan).
Thank you for reaching out and reporting the blacklisted IP issue!
Sparkpost IP’s can get blacklisted for a number of different reasons. A customer may not be following good data hygiene practices such as validating all of their recipient lists and as a result, they may hit a honeypot. A honeypot is a recycled email address ISP’s can use to monitor whether or a not a sender is legitimate or a spammer. Another reason why an IP can be listed is due to poor sending practices such as sending out prohibited content, unsolicited bulk email, and etc. We do our best to monitor anything sent through Sparkpost on a daily basis, however spammers and poor sending practices of other customers may affect the sending reputation of a shared pool as whole.
That being said, it is also important to note that we do actively monitor blacklists and any blacklists that affect our customers we work to resolve. There are literally thousands of blacklists for thousands of reasons and most of which do not affect you. We don’t spend our time on blacklists that do not affect our users or blacklists that will be automatically de-listed after a preset time. Major ISPs and Filters generally don’t use blacklists as they have their own scoring system.
I looked at IP’s you provided and they are listed on the following blacklists, CASA CBL, DNS Realtime Blackhole List, SORBS SPAM, and UCEPROTECTL1, which we consider to be minor actors as they are not reputable players in the anti-spam community. As well, they never respond to delisting requests, and often attempt to charge a fee for delisting. We have found that blacklistings by them do not impact sending in the vast majority of case
However, after a review of your account and sending history, we were able to make an adjustment to your sending pool. This change will take effect immediately for all new sends however, retries will continue to go out over the existing pool until they time out.
Should you have any further questions or concerns, please do not hesitate to reach out!
I think I have never received such an extensive and non-blah response from any support agent ever.
I followed up on this response because I was curious what kind of adjustments they made to “my” IP pool. I also asked whether they had higher and lower quality IP pools and how they decided to move customers from one to another. Their response came within less than an hour:
The adjustment I made was to move you into a new sending pool that was showing improved deliverability rates. We make these types of changes based on a number of different factors and if everything looks good, we move you into a different sending pool.
Overall, I would say it’s not about higher vs. lower quality pools because the sending reputation of each IP in the various pools can change hourly or day by day just based on what kind of activity goes through each one. For example, if Pool A with 3 IP’s had a 100% deliverability rate but an SP customer was sending bulk Rayban spam, then the IP that was used to send out the spam will obviously get reported and put on a blacklist. But again, we do our best to monitor and resolve blacklists that do affect our customers and actively educate everyone on sending best practices!
Hopefully this answers all of your questions, otherwise please let me know if there’s anything else you need.