Hi, I'm the product manager on Postmark, and wanted to chime in with a bit more of our rationale for mostly using shared IPs. With our exclusive focus on transactional email and high deliverability, an existing reputation is extremely important. By using shared IPs customers can leverage our reputation, which we police and protect heavily. And since transactional email has better engagement overall, it increases our deliverability even more. Most senders don't need dedicated IPs since an IP with no reputation is worse, so we believe it's better for the majority of our customers and their deliverability to use shared IPs.
That said, there is a case to be made for very large senders to have their own IPs. We agree with that. Our point is mainly that the vast majority of senders don't need it, and should rather use the stellar reputation of our shared IPs to ensure good deliverability.
The rationale seems to be that shared IPs are cheaper for them (and the customer). It's also possible that Postmark doesn't have the capacity to operate a large number of dedicated IPs for individual customers.
Any large-scale sender for whom deliverability is critical should be using a dedicated IP. By virtue of hosting multiple customers, shared IPs appear to send more frequently, and any behavior on a shared IP resulting in a blacklist entry affects everyone else on that IP.
We're pretty aware of this problem at SendGrid. Even though we make every effort to cull bad senders from our shared pools, our enterprise senders nearly always prefer dedicated IPs, which let them build up a trusted reputation without interference from others.
If we only send a few hundred emails a month, but need everyone to reach customer's mailbox (transactional emails, not marketing emails), would you recommend a dedicated IP? how would I know if the dedicated IP has ever been/is blacklisted too?
We're using Mandrill, but we am looking at alternatives longer term.
If you're only sending a small amount of desirable transactional email, you're the perfect model of a good sender and your blacklist risk will be vanishingly low. Sending from a shared IP will still expose you to the behavior of the other customers using it (like a VPS, you'll have neighbors). We actively police our shared IPs for bad sender behavior.
Dedicated IP packages won't be affected by the sending habits of other users. They are more cost-efficient for high-volume senders, but we do have dedicated IP tiers starting at the $80/mo. mark, which allows up to 100k mails a month.
With either option, we're always happy to work with you if you're having deliverability issues - and that includes checking IPs for blacklist status.
Postmark App has been very effective for our platform. Very little gets flagged and they have an easy way for users to "appeal" and have their emails approved. The only thing (good and bad) is that if a vendor erroneously flags our emails to our provider team as spam, Postmark won't event attempt to deliver it. It's a hard no. So, we have to have an email sent from that address to Postmark to (in essence) re-subscribe /verify that they want the emails to come through. This happens even though people aren't manually flagging them as spam, it's something on Y!, Gmail, Hotmail, etc. are doing on the back end.
I think they present a reasonable argument (and their methods obviously work for them), but I don't agree with them 100%.
They present several arguments both for and against dedicated IPs. From my own experiences, I don't believe that the "cons" outweigh the "pros".
FTA:
> By offering a dedicated IP for the majority of customers the ESP is basically saying “You do what you want, if you get blocked it’s your fault.” It also places a lot of heavy lifting on the customer, which defeats the purpose of paying for an infrastructure product in the first place.
No, by offering a dedicated IP the ESP is saying, "I don't want ONE customer to ruin things for all other customers". It doesn't one you can be careless or not take basic safeguards. It means that any "fallout" is contained and collateral damage is minimized.
> In addition to this, new dedicated IPs are just as bad as IP addresses with a bad reputation, since it has no reputation at all.
I'm not sure that's the case. Anecdotally, I've brought up additional mail servers at times and put them into service without doing any "warming up" and not ran into issues. My servers aren't sending out any bulk mail, however, so perhaps this is why it hasn't been an issue.
> The other misconception with dedicated IP addresses is that each one is completely independent. For instance, if one customer gets blocked, all other IPs are fine, right? Wrong. ISPs and blacklists will monitor entire IP ranges and domains. If one IP causes enough problems, traffic from the entire subnet or domain could be blocked.
Yeah, some of the RBLs as well as myself sometimes block ranges. That typically only happens when there are $bignum IPs in that range that have already been blocked. Pretty much everyone blocks individual IPs at first. If it happens that, for example, I end up blacklisting 15 IPs out of a /24 (allocated to somewhere in China, perhaps) then yes, I'll often just list the whole /24 instead. That's not the first step, however.
> The final reason, and this one is important, is that ISPs are starting to place a lot of weight on domain reputation, not just IP reputation. My guess is that over time IP reputation will slowly fade away while more weight is given to domain reputation along with authentication standards like DKIM.
I certainly agree that domain reputation is becoming more important. It's not an "either or", however. While the reputation of the sending domain (assuming valid DKIM signatures) is certainly one factor to consider, IP reputation isn't going away any time soon. Domain reputation is just an additional attributes that will be considered when making the "spam/not spam" decision.
One certainly shouldn't use IP reputation, in isolation, to make that "spam/not spam" decision but as just one variable in the whole formula. The first time I blacklist an IP, it's automatically removed after 12 hours. Shit happens sometimes, even with many protective measures in place. Every subsequent time a "repeat offender" gets listed, however, the length of time it remains listed grows until, eventually, it just stays on the list. In addition, as mentioned above, ranges sometimes gets listed as well. A quick glance shows that the largest netblock I've listed is a /12, as well as a handful of /15s and /16s, but those are exceptions. The overwhelming majority (of ranges) are /24s or smaller.
https://postmarkapp.com/blog/the-false-promises-of-dedicated... (Edit to add url)