See also Change Your Zimbra Password

See also Zimbra Password Policy

This should work on Zimbra OSE 8.8.15 and on Zimbra 9.0.0 OSE (Zextras Open Source Build)

Log into your Zimbra server as root.

cp -a /opt/zimbra/jetty/webapps/zimbra/public/login.jsp /opt/zimbra/jetty/webapps/zimbra/public/login.jsp.orig

vim /opt/zimbra/jetty/webapps/zimbra/public/login.jsp

Search for:

domainInfo.attrs.zimbraFeatureResetPasswordStatus

Move this line down:

<c:if test="${domainInfo.attrs.zimbraFeatureResetPasswordStatus eq 'enabled'}">

immediately above this line:

</c:if>

The Forgot Password link should now be visible on your Zimbra login page.