CPU/RAM requirements for Exchange Server SE if only being used for Entra sync & SMTP relay?

Since we run local AD with Connect Sync to Entra and have a need for an on-prem SMTP relay for our network device alert emails, etc it seems we will have to keep a single Exchange server on-prem to facilitate a smooth connection to our 365 mailboxes. If no actual mailboxes are being hosted on it and it's only used for Entra sync and SMTP relay (typically only a handful of emails per day but can burst to a couple hundred during a big outage), how much CPU/RAM does Exchange SE really require to run?