Redirect to gmail not working

[#1]

As google are dropping POP3 access to external email, I am trying to redirect my plus net email to my gmail account.

I have added a redirect for a new mailbox name to my gmail address but nothing sent to the new mailbox gets delivered.

Am I missing something or will this never work?

[#2]

Email redirect has largely been killed off by the introduction of SPF.
SPF defines a list of approved IPs for the ISP's outbound email servers related to the original sender.

The issue is a redirected email arrives with the original sender's email address but is delivered via say a Plusnet outbound email server. 

The gmail platform detects the SPF records for the original sender do not match the IP of the Plusnet email server
and the email is classed as forged. it may be discarded or rejected back to the original sender.