If possible, avoid using UUCP. For an explanation, refer to http://www.sendmail.org/m4/uucp_mailers.html or do a search in /etc/mail/cf/README on this string: USING UUCP MAILERS.
UUCP defines these mailers.
Names in the $=U class are sent to uucp-old. uucp is the obsolete name for this mailer. The uucp-old mailer uses an exclamation-point address in the headers.
Names in the $=Y class are sent to uucp-new. Use this mailer when you know that the receiving UUCP mailer can manage multiple recipients in one transfer. suucp is the obsolete name for this mailer. The uucp-new mailer also uses an exclamation-point address in the headers.
If MAILER(smtp) is also specified in your configuration, two more mailers are defined.
This mailer uses domain-style addresses and, basically, applies the SMTP rewriting rules.
Names in the $=Z class are sent to uucp-uudom. uucp-uudom and uucp-dom use the same header address format, domain-style addresses.
Because the smtp mailer modifies the UUCP mailer, always put MAILER(smtp) before MAILER(uucp) in your .mc file.