Support for socks4/5 is a compile time configuration option. Once
compiled in, fetchmail will always use the socks libraries and
configuration on your system, there are no run-time switches in fetchmail
- but you can still configure SOCKS: you can specify which SOCKS
configuration file is used in the SOCKS_CONF environment variable.

For instance, if you wanted to bypass the SOCKS proxy altogether
and have fetchmail connect directly, you could just pass
SOCKS_CONF=/dev/null in the environment, for example (add your
usual command line options - if any - to the end of this line):

env SOCKS_CONF=/dev/null fetchmail