Tune spam filtering and trusted senders

Choose Mail flow, then Spam & senders.

Start with the standard level. Raise it only when too much spam arrives, and lower it when real mail is held.

Deliver it to the Junk folder with a flag, or hold it in quarantine so it can be reviewed.

Add a domain or address to always trust or always block. Mail from a trusted sender still faces authentication checks, so forged mail is caught.