In order to improve your email delivery and to have better looking tracking links in your emails, you can setup a custom domain and use it in Signitic.
In order to setup this domain, you have to follow a process unique to each hosting client. Here is a small list for the some of them.
Basically, you have to follow majors steps that are:
Create a new DNS record. (example: track.mydomain.com)
Choose CNAME as a type of record.
Enter custom.signitic.app as the value.
Once your CNAME is setup, you should see this screen when you try to access your subdomain (example: track.mydomain.com):
When the DNS record is saved on your hosting client, you only need to fill the field with your record in Settings then Custom tracking domain.
Don't forget to save it and next signatures update, your domain should change.