Mailing to corporate domains

One of the struggles of delivery consulting is doing ISP relations and problem resolution for clients attempting to mail to corporate domains. The rules for getting mail into ISPs are generally pretty clear, and if they’re not I can typically find someone there who will give me the time of day. At corporate domains, though, all bets are off.
While ISPs strive to deliver wanted mail to their customers while protecting them from spam, businesses have different goals for email. For most businesses email is a tool. Mail boxes belong to the business, not the employee. In many cases, businesses do allow personal use of email so some marketing mail to employees is acceptable. However, if a corporation blocks personal marketing email, they are less likely than commercial ISPs to let even legitimate email through.
Large corporations typically run their own mail systems. Once a sender is blocked, however, the corporation will not unblock their email unless the sender can demonstrate that the mail is business related.
Smaller businesses typically use commercial appliances or filtering services. In these cases there is less need to justify the business related nature of email. Unfortunately, some commercial filters do not listen to senders or provide block resolution. At least one filter claims that the only way you can deliver mail to their users is for the users themselves to whitelist the sender.
Businesses of all types are much more security conscious than home users. Some “spam” blocking may be more related to security than actual spam. Finally, there are workplace and environment issues. Companies may be liable under the hostile workplace laws if they allow porn or other offensive emails into their employee mailboxes. One company I know of blocks any email with the word “viagra” in it. The email administrator of said company says that in the years this block has been in place there has only been one false positive… and that employee was told his wife should not use that word when emailing him shopping lists in the future.
All of these issues make it difficult to troubleshoot delivery problems at corporations.