Wordpress subscribe.url not using base page
SOLVED at https://lab.civicrm.org/dev/wordpress/issues/27/



Old workarounds:

I tracked down the problem somewhat and opened an issue at the bug tracker.  I describe a code change which makes this work...but I don't know whether it's the best solution.

https://issues.civicrm.org/jira/browse/CRM-20053

UPDATE: I couldn't get that old fix to work any more after upgrading to CiviCRM 4.7.21.  So I put in an Apache rule in my .htaccess file to redirect:

&lt;IfModule mod_rewrite.c&gt;
RewriteEngine On
RewriteCond %{REQUEST_URI}  ^/wp-admin/admin\.php$
RewriteCond %{QUERY_STRING} q=civicrm/mailing/confirm
RewriteRule ^(.*)$ /civicrm [L,R=302]
&lt;/IfModule&gt;