Hardly any. To reduce this number even further you can whitelist certain newsletters, top candidates for being erroneously classified as spam.
To make sure About newsletters always get through uninterrupted, whitelist "about.com" in SpamAssassin.
Whitelist a Sender or Domain in SpamAssassin
To whitelist individual addresses or domains in SpamAssassin:
- Open /etc/mail/spamassassin/local.cf in your favorite editor for system-wide whitelisting.
- To whitelist only for yourself, open ~/.spamassassin/user_prefs.
- Append "whitelist_from_rcvd {address or domain you want to whitelist preceded by "*@"} {domain name which must be present in the Received: headers}".
- To whitelist all About newsletters, for example, type "whitelist_from_rcvd *@about.com about.com".
The second parameter of whitelist_from_rcvd, a domain name which must be present in the Received: header lines, is some prevention against spammers easily getting past SpamAssassin by using an email address at a commonly whitelisted domain.
