With multiple Gmail accounts, it's often easier to forward all emails to a single main account that you actually check. This can be accomplished by setting up a forwarding account in Gmail's settings.
However, something that isn't immediately obvious is that messages that are considered spam are never forwarded. While Gmail's spam detection is extremely good, it's not perfect. There have been times where emails that I actually wanted have ended up in the spam folder and weren't forwarded to my main account.
To fix this, we want to tell Gmail to not flag anything as spam so it will be forwarded along.
Note
This will not cause spam to appear in your inbox. It bypasses the spam filters so the email is forwarded properly, but the account it's forwarded to will also flag the email as spam. The end result is that that the email will end up in the spam folder of your main account (where you can actually look at it) instead of not being forwarded from the original account at all.
We can do this with a filter that matches is:spam and applies the option "Never send it to Spam".
Unfortunately, Gmail's interface makes this task much harder than it needs to be.
- Open Gmail and do a search for
is:spam. Notice that Gmail autocorrects it toin:spam. - Click the dropdown arrow on the right side of the search box to bring down the advanced options
and click "Create filter with this search". Hit "OK" on the warning box that pops up. Notice that
the filter has been autocorrected again to
label:spam. - In the URL you should see something like
#create-filter/has=label%3Aspam. Changelabeltoisin the URL and hit enter. It should modify the text in the box without changing anything else. - Check the "Never send it to Spam" checkbox and hit "Create filter". You'll see the text get
autocorrected to
in:spamagain, but if you check in Settings -> Filters and Blocked Addresses you should see the correctis:spamfilter.