ESP emails can be sent from two geo locations, EU or US. Selecting the email sending region is a part of the initial client setup and can't be easily altered afterward (as it requires certain migration steps, including potential client's assistance).
In each of the geo regions there are 2 options for selecting IP addresses used for sending emails: shared sending IP address pools and customer-dedicated IP addresses. Using dedicated sending IP addresses is an add-on option that has to be agreed upon with a Piano Account Management team representative responsible for interactions with the customer.
Dedicated sending IP addresses offer the best isolation in terms of deliverability metrics, where the customer is solely responsible for their own delivery quality: the cleaner the sending practices - the better sending reputation for a customer would be, and vice-versa.
On the other hand, customers with low and irregular sending patterns should refrain from using dedicated sending IP addresses, as it may cause unexpected deliverability problems.
The default option of using shared sending IP addresses is, overall, the best starting point for any customer: it offers the sending of emails through IP addresses with a good reputation and is not vulnerable to problems associated with irregular sending patterns. The reputation of shared sending IP addresses is proactively monitored by Piano and in case any sending reputation degradation takes place active measures are taken to restore the reputation or remove the affected IP addresses from the pool.
In case any customer is seen to not adhere to the recommended sending practices (mailing list collection and proper content distribution), Piano would normally contact the customer after receiving certain internal alerts noticing abnormally low email delivery metrics or being notified by upstream email providers about improper sending behavior. In this case, certain suggestions are made with regards to what the customer has to do in order to maintain a good sending reputation.
In case the customer does not change their sending practices, Piano would remove such customers from a good-standing shared IP address pool and place them in a non-monitored IP sending pool (with no measures taken to improve any deliverability issues) until the mentioned actions are taken by the customer. As soon as the corresponding measures are taken and Piano is able to verify a good track record of quality email sending, the customer may be brought back to a normal shared IP address pool.
The transition of a customer between sending pools does not usually apply to the case when a customer uses dedicated sending IP addresses as there the customer is responsible for their own deliverability, not affecting anyone else and not getting affected by anyone in turn either.
The list of IP addresses in each pool used for a particular pool or customer is fairly static but still can change from time to time (due to IP addresses being added/removed/rotated, etc.). A specific list can be obtained by contacting Piano Support at support@piano.io.