Pretty tough, based on what 168 IT executives of major North American companies told Forrester Research in a study sponsored by email delivery consultant Return Path.

Here's what you're up against when you send email to corporate addresses. Since the numbers add up to more than 100%, you can assume companies are using more than one tactic to block suspect email:

1. 61% of IT execs said they use a readymade commercial filtering application or appliance.

2. 49% said they create their own rules to block spam based on message weight /size, keywords, attachments or message type.

3. 37% said they run each message sender through their own blacklist, while 34% said they use public blacklists. The most frequently cited blacklists are Mail Abuse Prevention Service (MAPS), Open Relay Database (ORB), SPEWS, SpamCop, Spamhaus and WireHub/Easynet.

4. 27% use a client-side application like Norton Anti-Spam (about a quarter of respondents said they use that application, the largest single bloc in the study)

5. 10% use an open-source application like SpamAssassin.

A couple other findings:

-- Nearly half of respondents who filter say they customize the settings on their filtering application or appliance to be more stringent than the default settings.

-- 23% of the people who said they use a public blacklist to screen out spammers didn't know which blacklist they use.

Return Path has packaged the findings in a free three-page whitepaper which you can download here.