If you want you can manually configure spamassassin, but you will still need to know why the mail was classified as spam. It’s still good to check out the headers.
Start by crearing a local configuration file to spamassassin.
- create a file like
/etc/spamassassin/90_custom.cf - add a line
whitelist_from <emailaddress>in the file
This should whitelist emails coming from that email address. There’s more subtlety here, e.g. look at whitelist_from_spf and whitelist_from_rcvd if you’re interested in having better controls over whitelisting. The other way around is also possible, by using blacklist_from
Look at the spamassassin documentation for more details.