Email as a communications mechanism is very much in use today despite the multiple other alternatives available, and as such still is plagued by a lot of spam.
In November 2018 over 85% of the emails were spam which means spam prevention is still very much crucial.
One methd to apply to the mix if spam bypasses the default antispam solutions is a manual email filter.
The filter can be set to deny any perceived spam email, this an attempt in making the sender aware of their email being regarded as spam.
This is however futile as a majority for spam appears to be from dodgy domains or exposed mail servers, these have very little chance of their postmaster taking the appropriate actions to resolve spam transmissions.
The best handling of spam, that eludes the typical spam prevention solutions in place, is to simply identify unique traits in spam filters and then discard them.
This silent approach is only logical as there is extremely little chance that anyone actually takes not of emails that are rejected due to spam.
It is worth mentioning that having a look at your discarded emails is a good idea as you might experience "false positives" occasionally.
With any decent email client you can configure rules to handle emails that the normal spam protection solutions flag, email that is if they are not wiped out directly.
These spam emails can be stored in a folder for reference use should you not have the rule to simply delete them.
Such a folder of shame can provide valuable insight into how efficient the anti spam solutions in place are, but also offer insight into content patterns allowing for better filtering in order to discard at the gates even more spam.
Spam that eludes both your filters and anti spam solutions should upon discovery be submitted to a suitable service such as Spamcop. This feeds back informtion about spam that improves blacklists.
