With further investigation, we now have a much more detailed picture of the cause of the segment calculation delays. Since around 05:15 UTC 16 August 2018, one of the databases responsible for processing segment calculations has been experiencing fluctuating performance issues. Based on the data we have available, this appears to have had a particular impact from 09:00 UTC 16 August until 14:00 UTC 16 August and again between 09:00 UTC and 14:00 UTC 17 August. We did observe issues on the 16 August, yet the impact was not significant and we made immediate configuration changes in response to this that we believed had rectified the issue. The reoccurrence on the 17 August was much more significant and has given us more data to understand this issue. Firstly we want to clarify this has *no impact* on automated Workflows, Transactional or Behavioural emails. The impact of this issue has manifested in three ways (and has not affected all customers): 1. Newsletters being delayed, waiting for our system to ensure a segment is up to date. 2. New segments created not calculating at all in the UI and returning 0. 3. Segments taking a lot longer than normal to calculate. This may also be evidenced by a lack of "calculation" bar in the UI despite you having selected "Refresh" In response to this issue, we have made some further changes to our cluster's configuration. At the present time, segment calculation appears to have returned to near-normal, though we are not yet comfortable that the situation has returned to normal, and we will be observing the impact today and Sunday to ensure things have improved. We are doing all that we can to ensure segment calculation times are normal and that there is no short term impact. All segments that were delayed yesterday have been successfully calculated. Our data also shows us all newsletters were sent as expected. If you see anything anomalous or unexpected in your account, please email us at email@example.com so we can investigate. We are also happy to answer any questions. We apologise for the inconvenience caused.