MySQL mailuser not being allowed in

I created a new user with the following line from the Linode guide "EMail with PostFix, DoveCot and MySQL", the MySQL section, step 4.

GRANT SELECT ON mailserver.* TO 'mailuser'@'127.0.0.1' IDENTIFIED BY 'asdf';

When I inspect the user table, I get the following:

mysql> select host, user, select_priv from user;
+-----------+------------------+-------------+
| host      | user             | select_priv |
+-----------+------------------+-------------+
| localhost | root             | Y           |
| localhost | mysql.session    | N           |
| localhost | mysql.sys        | N           |
| localhost | debian-sys-maint | Y           |
| 127.0.0.1 | mailuser         | N           |
+-----------+------------------+-------------+
5 rows in set (0.00 sec)

Shouldn't the select_priv field hold a "Y" for 'mailuser'?

When I exit mysql and try to re-enter as 'mailuser' I get the following error message.

fgphil@adonax:~$ sudo mysql -u mailuser -p
Enter password:
ERROR 1045 (28000): Access denied for user 'mailuser'@'localhost' (using password: YES)

I am wondering about MySQL asserting "localhost' here, especially when I've explicitly used '127.0.0.1' as the host of mailuser.

Does this indicate that I've done something wrong with my hosts file?

The /etc/hosts file current has the following lines (with XXX to obscure the actual ip address).

127.0.0.1 localhost
XXXIPv4XXX adonax.adonax.com adonax
XXXIPv6XXX adonax.adonax.com adonax

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

If I create the MySQL user with a host of "localhost" instead of "127.0.0.1" I am able to get into MySQL as mailuser, and run select queries, despite the "select_priv" field for mailuser holding a "N". Why is this?

I would like to conform to the guide and use mailuser@127.0.0.1 instead of mailuser@localhost, if possible. There are commands further on in this guide that might be affected if I start changing things, I fear.

I should mention, I tried editing the first line of the hosts file to read the following:

127.0.0.1 localhost.localdomain localhost

But this doesn't seem to make any difference.

Is there anything special that has to be done after editing the hosts file to make it operative? For example, exit and reenter the Linode? Shut down and reboot the Linode?