Create Gmail Filters
-  To make sure your mail server will not accidentally discard
important messages from our class as spams, you should establish a
message filter.
 -  Take Gmail for example, you may go from the Setting, and then
choose Filter.
 
.
 -  Click the link "Create a new filter".
 -  In the "From" field, type "ipv6.club.tw", and click "Create filter
with this search".
 -  Check the item "Never send it to Spam" and click the button "Create
filter".
 -  This will teach Gmail not to dispose messages sent from this server
as spams in the future.
 
Reference:
-  Using
Filters