Kirim is excellent for bulk sending of emails to lists or even just one individual! I have been using it since 2010 when we were first getting started in eCommerce but was only able to use their basic plan at that time (which did not include any advanced features). It used to take forever to send out new messages after changing something like date range etc - today this happens almost instantly!! The price has gone up over the years so you get what you pay for but there are some great benefits included such as being able to do A/B testing easily too which really helps us improve CTRs without needing expensive split tests. Sending large amounts of mail can be very tedious especially if your targeting long running sales cycles where people may need more reminders than they might otherwise receive from other channels.