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Send Time Optimization FAQ

Which plans offer Send Time Optimization?

STO is available on our Scale and Enterprise plans. Check out more detailed plan information here.


Do I have to have Open and Click tracking enabled with Mailgun for this to work?

STO will work best with Open and Click tracking enabled, however, we do aggregate the data at the Mailgun level, so Open and Click tracking is not required for STO to work.


What happens if there is no engagement data for a recipient?

Given the number of messages we send on a regular basis, chances are pretty good that we’ll have some engagement data for your recipients to analyze and make a decision, however, this may not always be the case. If we don’t have any engagement data, or the data is not sufficient to make a confident decision, the message will be delivered at the originally scheduled time (immediately if the message is not scheduled).


Will this improve my delivery and deliverability rates?

Short answer: no. Delivery rate is the measure of the number of messages sent vs the number of messages that actually get delivered (and not bounced) to a mailbox (regardless of whether it made it to the inbox or spam/junk folder). Deliverability rate is the measure of the number of messages that were delivered vs the number of messages delivered to the inbox (and not spam/junk). STO will not improve these rates. If you already have high delivery/deliverability rates, what STO should do is improve your engagement rates for messages that are already being delivered to the inbox as they should be more visible to recipients.


How do I see the scheduled messages that were sent using STO?

Assuming you tagged the STO message using a unique tag, you can perform a search in the logs for tags: “<tag>” and you’ll see a “scheduled-for”: 1568391126. The scheduled time is displayed in epoch time, which you can translate using an epoch conversion tool like this one. The timestamp in my example (1568391126) translates to Friday, September 13, 2019 11:12:06 AM GMT-05:00 DST.


What type of messages should I apply STO to?

STO will work best for marketing messages that you want delivered when the recipients are typically engaged in their mailbox. Typically for transactional messages, you want them delivered immediately, or at a certain time, so we don't recommend using STO for transactional messages.


Can I use only my own Open and Click data?

No, not at this time. Our algorithm will analyze data that we’ve accumulated across all senders on our platform. 



Can I provide an email address and get back the optimal time?

No, STO will only schedule a message given the data we have on hand. The API will not return any data about the recipient


Can I turn it on via the control panel?

Currently, the only way to enable STO is via API parameter or SMTP header per message.


Can I use STO with a mailing list or batch calls?

Currently, STO is only available on a per recipient basis.