Here we provide step-by-step instructions on how to do it in Gmail by creating a filter:
1) Login to Gmail, click on the gear icon and select "Settings":
2) Select "Filters and blocked addresses":
3) Scroll past all your existing filters and select "Create a new filter":
4) Add the email address that you want to whitelist to the "From" field. Here we added monitor@downtimemonkey.com to make sure that we never miss a 'website down' alert:
5) Check the "Never send to spam" box and click "Create Filter". The email address will now be whitelisted!
In 'Step 4' we whitelisted a single email address. It's also possible to whitelist all emails from a domain.
By adding @downtimemonkey.com to the "From" field instead of monitor@downtimemonkey.com we would whitelist every email address belonging to downtimemonkey.com.
To whitelist more than one email address simply add each email address separated by the pipe symbol. For example, "monitor@downtimemonkey.com | verify@downtimemonkey.com".
The pipe symbol is a vertical bar '|' that can be added with shift and backslash on most keyboards.