The names listed for the two Post Office Protocol port
numbers in the /etc/services file are wrong according to RFC
1700 (at ftp://ftp.isi.edu/in-notes/rfc1700.txt).  The
/etc/services file shows the names for ports 109 and 110 as
"pop-2" and "pop-3", respectively, but their official names
are "pop2" and "pop3".  This incompatibility makes it
difficult to write portable software.  I recommend changing
the relevant lines to look like this:

pop2   109/tcp   pop-2 postoffice   # POP version 2
pop2   109/udp   pop-2
pop3   110/tcp   pop-3              # POP version 3
pop3   110/udp   pop-3