I want to send all HestiaCP system mails (credentials for new db, user, backup, notifications about updates, etc) with a gmail account via SMTP for having a valid sending mail. I try this from VestaCP but all mails go to spam folder.
so your modification is working then and your mail get send through grmail as it seems.
mail going to spam means they are delivered but on the receivers end they are categorized as spam for whatever reason. we can’t help with mail reputation though, that’s not neccessarily a thing you can just put into a setting
try to find the real reason, most likely the mail from that gets set for those differs the mail account used and this leads to a malus when the box is checking for spam characteristic. could be a lot of other things as well though.