Mail does not sync: Outlook and phone

It syncs, just not yours

First learn which account type you have: IMAP and Exchange sync both ways, POP3 downloads and usually deletes from the server. Half of «mail disappeared» tickets are POP3 on a second device eating everything. If the account was set up years ago as POP3, recreate it as IMAP before touching anything else.

Stuck outbox and duplicates

One oversized attachment wedged in the outbox blocks everything behind it: delete it (or move it to drafts), then send smaller. Duplicates arriving in pairs point at «leave copy on server» plus a second client fetching the same box — pick one fetcher.

The webmail test

Open the same mailbox in the browser: if webmail works, the server and password are fine and the fault is purely local client config. If webmail fails too, reset the password and re-check — client settings cannot fix a dead account.

Mailbox full behaves like broken sync

A quota-full mailbox rejects new mail silently on some servers and loudly on others — either way the client looks «stuck». Check usage in webmail first: over 90 percent means archive sent items and clear the deleted folder before touching any setting.

Phone-only sync failures

Desktop fine, phone stale: background refresh killed by battery optimization, or an ancient saved password after a forced reset. Re-allow background data, remove and re-add the account (it takes two minutes and fixes most phone-side corruption), and keep the OS mail app updated — vendors quietly drop old auth methods.