Persistent and Non Persistent SMTP


This write-up marks the starting of a new blog series called “What’s New”. Under this particular category, we will be discussing new feature additions, add-on tweaks and related software updates. The first blog of this series discusses how to keep SMTP connection persistent and alive for Batch Sending  and how to use currently available SMTPs in a Loop, during the warm up session.

Most of you might already have updated your Mumara to the latest version, but if you still haven’t updated it, do it today. Few previous updates have added a little extra, in terms of convenience, usability and user experience. Towards the 3rd step of “Scheduling Email Campaign” you will notice couple of choices for SMTP Sequence. This new addition will enhance your control to choose between “Batch” and “Loop” sequence of selected SMTP accounts.


Do you want to send fast and bulk? Batch sequence of SMTP will help you to keep SMTP connection alive. Persistent SMTP connection eventually results in preventing unwanted delays in sending. Selection of this option will automatically set the batch sequence. Dividing number of emails in the campaign to send by number of selected SMTPs. The maximum batch size is 500 emails per SMTP. It means, you can keep the SMTP connection persistent for the batch of 500 email sends. Let’s take an example of custom configured mail server to understand more about “Batch” sequence of SMTP.

The example server has 5 IPs, each SMTP is configured with one separate IP and you eventually have 5 SMTP accounts within Mumara. The campaign you are scheduling is set to reach 1,500 subscribers, you have selected 3 SMTP accounts from the available 5, and “Batches” is selected sequence of SMTP.

It will establish connection to the first SMTP that will remain alive, until it finishes its batch of 500 emails. Once the first SMTP connection is closed, the persistent connection with the second SMTP is established to send its batch of 500. It is how it works for the maximum batch size.  End result of this type of SMTP sequence will help reducing sending time to a large extent.


Are you sending IPs warm up campaign? Batches may not be the fitting choice of the SMTP sequence, when the IPs are new and you are trying to increase sending reputation. In this case, you may need more frequently rotating SMTP connections. “Loop” is the suitable choice of SMTP sequence. Let’s take the aforementioned example of custom server, when the “Loop” sequence is checked as preferred choice, among the 5 SMTP accounts, 3 are selected to send 1,500 emails.

It will take first SMTP and will close the connection after sending the first email, the next SMTP will send the second email and the third will send the third. This cycle repeats from 4th email, and the loop behavior continues, until it finishes 1500 emails. Even in this case, each IP will send 500 emails, but the SMTP connection will not remain persistent.

This SMTP sequence suits best when you want to limit your sending speed and time, in the midst of most crucial phase of IP warming or improving sender scores. This option gives enhanced control to automatically switch among SMTP connections by setting up sending limits. So this addition of SMTP sequence can really help to customize sending pattern according to your need.