I upgraded a test Hestiacp server to debian 12 last week as a test for any issues and all worked perfectly including SRS, the updated exim4.conf.template file magically appeared along with srs.conf file and just worked.
Today I upgrade my live Hestiacp server, all seems to have gone well except for SRS, there is no SRS.conf file or the template not updated i’ve also uploaded the new exim4.conf.template, I restarted exim4, restarted hestia and still no srs.conf, no matter what I do.
Create a mail account in HestiaCP and add a forward mail address to an external domain like an account you could have in gmail.com. Send a mail to your HestiaCP mail account and wait for the mail arrives to your gmail account. In gmail you can view the headers and SPF info using more (three dots) -> show original.
There you will see whether you have passed SPF check (that should be a good check to know srs works) and in the headers you will see several headers containing srs0= .