Automated Custom Emails Sent Around Dates

Need software that enables us to send multiple emails to specified people on a specified schedule that merges data into each email. The goal here is to schedule events with supporters for a specific date, and then have custom emails sent to them before and after that date to remind them and give them information. For example, the event might be for October 10, 2017, which we will label as “EVENTDAY”. Today, August 29, 2017, would be labeled as “STARTDAY”. We want to be able to set up a series of automated emails that go out on a schedule that revolves around the EVENTDAY or the STARTDAY. For example, we want an email to automatically go out two days after the STARTDAY. It may say something like, “Thanks FIRST LAST, for agreeing to hold an event on EVENTDAY.” The customer will see, “Thanks Bob Smith, for agreeing to hold an event on October 10, 2017.” Then, we might want an email that goes out automatically 4 days before the EVENTDAY that says, “Hi again FIRST, just a reminder that your event will be on EVENTDAY at TIME at LOCATION.” Then we have another letter that goes out 4 days after the event that might say, “Thanks for holding the event for us, FIRST!” Further, on some days, we will want to send an additional email to our own email addresses, saying something like “Hey, don’t forget about FIRST’s event on EVENTDAY”. We have about 22 unique fields, in addition to the email address of the receiver. We have about 20 email templates that have to be sent out on the dates we specify, each with fields that need merged with the unique fields. Your solution should automatically calculate the dates in which each of the emails are sent once we provide the STARTDAY and EVENTDAY. You may use Gmail APC functionality, or whatever else accomplishes this. Please keep in mind that we will need to use this program over and over for many different events. Thus, once it is run, it needs to schedule all the emails at that time, preferably through Gsuite. Scheduling them now will also enable us to verify functionality. All emails that are sent out need to allow us to specify the Subject line, and will contain our return address.