Gmail

Gmail on Android is a general-purpose mail client, not only a client for Gmail accounts. That is the fact most people do not realise: it handles Outlook, Yahoo, and arbitrary IMAP accounts alongside Google ones, which makes it a reasonable single inbox.

Storage is shared, and that catches people out

The 15 GB on a free Google account is shared across Gmail, Drive and Photos. Mail is usually not what fills it — backed-up photos are. But when the quota fills, incoming mail stops being delivered, and the cause is rarely obvious from inside the mail app.

If you are near the limit, checking Photos before deleting mail is usually the faster fix.

Settings that matter

• Conversation view can be turned off. If threading has always bothered you, that is where.
• Sync days defaults to a limited window on some setups; older mail is then only visible online.
• Notifications can be set per-account and per-label, which is the only practical way to handle a busy work account alongside a personal one.

Offline behaviour

Gmail caches recent mail and queues sends while offline. The window is configurable but finite — long-haul travel with a large archive benefits from raising it beforehand rather than discovering the limit mid-flight.