Prior to V8.10 sendmail, the name of the SMTP and -bt rule-testing help file was sendmail.hf. Beginning with V8.10 sendmail, the default name is helpfile. To change back to the old name, perhaps for sentimental reasons, you can do the following:

define(`confHFFILE', `sendmail.hf')

If you redefine this name, you must also redefine the HELP_FILE configuration macro (HelpFile) so that the correct name appears in your sendmail.cf file's HelpFile option.