As a longtime Gmail power user who's managed dozens of accounts across projects and roles, I've found that juggling multiple inboxes across apps is inefficient. Desktop clients like Thunderbird or Outlook work, but Gmail offers a superior, streamlined alternative. In this guide, drawn from years of hands-on experience, I'll show you how to consolidate everything into one Gmail inbox for effortless access. For advanced techniques, check our Guide to Gmail for Advanced Users.
Let Gmail be your central hub for all email!
I've relied on Thunderbird for years—it's powerful and versatile. But after migrating fully to Gmail, I never looked back. Gmail eliminates profile backups, frees up RAM (since your browser runs anyway), saves gigabytes of storage, and delivers a consistent inbox across devices. Its legendary search, Google Labs add-ons (now evolved features), and browser extensions add unmatched power. It's transformed my workflow, and I recommend it wholeheartedly.
Gmail handles multiple accounts just like desktop clients, with auto-filled POP3 server details for popular providers, making setup a breeze.
To import from an old Hotmail account, for example:

For separation, enable Label incoming messages and create a label per account. Pair it with Archive incoming messages (Skip the Inbox). Later, I'll cover creating dedicated inboxes via labels.
Success prompts an alias offer for sending. Confirm via code sent to the account, or add later under Send mail as in Accounts and Import.

Gmail imports only inbox mail. For folders, move items back gradually and label on arrival—plan for bulk with care.
Options abound: Merge seamlessly with aliases for unified replies, or keep accounts distinct for work/projects.
For separation, enable the Multiple Inboxes Lab feature (now integrated):

A new Multiple Inboxes tab appears. My setup: Panel 0 for starred, Panel 1 drafts, Panels 2-3 projects, Panels 4 for imports—each max 10 conversations below inbox.

Leverage Gmail's search operators (full list here). Use labels from imports for dedicated panels.
Your result:

To tame the influx:
How do you handle multiple accounts? Share tips below!