Setting up Heysender with your Magento shop depends on whether what version of Magento 2 you are using. In this guide we will use version 2.4.6 as it has custom SMTP built into the administration panel. Earlier version will require installation of a SMTP plugin like Mageplaza SMTP.
To setup Heysender in Magento 2 version 2.4.6 start by logging into your administration panel and navigate to Stores > Configuration > Advanced > System > Mail Sending Options now you see the image below
Start by unchecking the box under Transport and change Sendmail to SMTP
Now you get a few extra options, which should look like the image below
Now uncheck Host and set the value to smtp.heysender.com
You may leave Port at 25. Or you can use port 2525 or 587 instead if you desire.
Leave Set return-Path to No
Username and Password need to be set to the values of the SMTP user you wish to use from Heysender.
If you have not yet created the SMTP user you wish to use, have a look at this guide.
Next change Auth to Login
And finally change SSL to TLS
Now save the configuration and you are good to go. Transactional emails sent through Magento, are now piped through Heysender.