The ticket reply notifications we get in from Syncro always fail Syncro’s own DMARC rules because there is a DMARC policy alignment issue between the email envelope return-path and the header’s from address. Regardless of whether you have your own SMTP server setup in Syncro or not, the ticket reply notifications and RMM alerts come from Syncro’s servers.
This may be why those emails are going to spam as every mail server that respects DMARC (including Google Workspace and Microsoft 365) will mark those Syncro emails as failing the DMARC.
We have a feature request here for Syncro to fix this. Maybe if enough people like it, this issue will get resolved.