By popular demand, we have removed the [Formstack] that preceded the subject line on incoming submission emails. The tag was originally introduced to make it easier to setup email filters for these incoming emails, but feedback indicated that it was more of a detractor than a help.
If you want to keep the tag for whatever reason, you can just change your form title accordingly. Note that the form title isn’t ever displayed to users of your form, so you can name your forms whatever you want.
If you have any comments or questions about this, feel free to contact us.