Things to Try

• Devise an error-handling rule that will detect an address that contains a username and an @ character but no host part.
• Is it possible to have text in the LHS that is literally $+, rather than an operator with the same characters?
• The client.cf file uses $#error to handle errors in rule set 0. Examine your site's sendmail.cf file to see if it is legal to use $#error in other rule sets.