I have active Gmail, Yahoo and Outlook accounts as well as three IMAP accounts from my start-ups.
I used Outlook (desktop client) to manage all these inboxes.
The problem was that spam became uncontrollable, specifically for my three IMAP accounts and for Yahoo.

I always thought Gmail was amazing at beating spam.
I can then continue to use Outlook to manage this filtered mail.
Here’s what I did:
Imported all the accounts into gmail.com viaSettings > Accounts and Imports.
Created a label for each account so they appear as their own mailbox on Outlook.
The method is to create a filter:options > Filter > Create new filter >e.g.
for all emails with yahoo.com in theto:field and direct into the corresponding label.
Kept the default Gmail setup for different tabs: Primary, Social, Promotions, Updates and Forum.
This isolates the mail that are important (i.e.
Primary) and it’s possible for you to glance through the rest whenever you want.
This system works superbly.
This defeats the purpose of the whole exercise!
Fortunately, there’s a clever hack around it: create a label to mirror the Primary tab.
Filter all emails that matchCategory:Primaryand direct to the new label.
Via this label, I can now effectively enter the Primary tab from any mail client.
Gmail takes its sweet time to import mail.
On clients like Outlook, Gmail is the only email account needed.
All the other emails you’ve imported with their corresponding labels will appear through it.
On mobile, I can now actually use the native Gmail app, which of course does support tabs.
After a week of use, I’m happy to report that spam is mostly eradicated.
I say mostly because Gmail does not do a complete job detecting spam of Chinese origins.
Switching to Gmail made a huge difference on mobile.
There are important drawbacks, however.
The biggest is that Gmail doesn’t play well with Outlook.
I suspect all local clients, not just Outlook, will suffer from these annoyances.
If you’re an Outlook addict, you may not want to follow in my footsteps.
Another issue I experienced was that Yahoo doesn’t work well with Gmail either.
Fetching Yahoo mail is rife with errors and delays.
So Yahoo mail that I received yesterday may not appear until today on Gmail.
Overall, I’m happy with the switch.