A phone that has been delivering mail for a year can stop without any visible change: the Gmail app opens, the old messages are all there, and nothing new arrives. Pulling down on the inbox sometimes produces the missing message immediately, sometimes produces nothing at all. Those two outcomes point at completely different failures, and the fastest way to tell them apart takes about twenty seconds.
Open mail.google.com in any browser first — a laptop, or the phone's own browser in desktop mode. If the message is not in the web inbox either, the phone is innocent and no amount of app settings will help. If the message is sitting in the web inbox, delivery worked and the break is somewhere between Google's servers and the app's screen. Everything below is organized around that split.
A note on the menu paths quoted here: Android and iOS both move settings between versions, so each path is marked with the platform Google or Apple documents it for. Where a device shows an ampersand in a menu name, the word "and" is used below.
When the Message Is Missing From the Web Inbox Too
Three account-level conditions produce a phone that appears to have stopped syncing, and all three are invisible from the phone.
The account is out of storage
A personal Google Account includes up to 15 GB of storage shared among Drive, Gmail and Photos. Google's storage documentation is unambiguous about what happens at the ceiling: "When your account reaches its storage limit, you won't be able to upload or create files in Drive, send or receive emails in Gmail, or back up photos or videos to Google Photos." For Gmail specifically it states that messages sent to the account go back to the sender.
The trigger is usually Photos or Drive rather than Gmail: a folder of video is uploaded, the account crosses the line, and mail stops days later with no notification the phone owner connects to the event. Check the storage figure at one.google.com/storage before touching a single app setting.
The long tail matters too. Google states that if an account stays over quota for 2 years, content across Gmail, Drive and Photos may be deleted, and that it will contact the account holder at least 3 months before content becomes eligible for deletion. An account that has been bouncing mail for months is not in a stable state.
A filter is archiving the message before it reaches the inbox
Gmail filters run on incoming mail, and one of the actions available when creating a filter is Skip the Inbox (Archive it). A message caught by such a filter is delivered, stored and searchable — it simply never appears in the inbox on any device. The phone is syncing perfectly and showing an inbox that genuinely does not contain the message.
Filters are managed at Settings → See all settings → Filters and Blocked Addresses, and Google documents filter creation on a computer only. That asymmetry is worth holding onto: a rule that changes what a phone displays cannot be inspected or edited from the phone. If mail from one sender or domain is the only thing missing, searching for that address in the app rather than browsing the inbox confirms it in seconds.
Forwarding is set to archive Gmail's copy
Gmail's forwarding setting, at Settings → See all settings → Forwarding and POP/IMAP, offers a choice about what happens to the local copy once a message is forwarded. The two documented options are keep Gmail's copy in the Inbox and automatically archive the copy. If the second was chosen — often years earlier, when a second address was set up — every forwarded message is archived on arrival and the inbox stays empty while the mail keeps flowing to the other address.
It arrived, but not in Primary
This one is visible on the phone rather than the web, but it belongs in the same group because sync is working correctly. With the default inbox type, Gmail sorts incoming mail into Primary, Social, Promotions, Updates and Forums. Google describes Updates as "automated confirmations, notifications, statements, and reminders" — which is precisely the category most people are waiting on when they say mail stopped arriving. Categories are toggled in the Android app at Menu → Settings → the account → Inbox type → Default Inbox → Inbox categories.
Android: Two Sync Switches That Do Not Talk to Each Other
If the message is in the web inbox, the next thing to understand is that Android has two independent sync controls for Gmail. One belongs to the operating system and covers the whole Google Account; the other belongs to the Gmail app and covers one address. Turning on either one does nothing for the other, and both must be on.
The Sync Gmail checkbox
Google's sync-error guidance for Android states it plainly: open the Gmail app, tap Menu → Settings, tap the account, and "Under 'Data usage,' make sure the box next to 'Sync Gmail' is checked." The description of that setting in Gmail's settings documentation explains exactly what the off state looks like: "When this setting is on, you'll get notifications and new emails automatically. When this setting is off, you have to pull down from the top of your inbox to refresh."
That is the signature symptom. If pulling down reliably produces the missing mail and nothing arrives on its own, this checkbox is the first suspect. It is per account, so on a phone with a work address and a personal address it can be on for one and off for the other on adjacent screens.
Days of mail to sync, and per-label sync
On the same Data usage screen sits Days of mail to sync, described by Google as "the number of days of mail that you want to automatically sync and store on your device." This does not stop new mail, but it changes what the app keeps locally, and on a phone that was configured to save space it can make the inbox look truncated in a way that reads as a sync failure.
One level up, Manage labels is documented as the place to "choose notification and sync settings for different labels." Mail that carries a label whose sync has been turned off will not be pulled down with everything else. This is an easy setting to change once and forget, and it produces the odd pattern where most mail arrives normally but one category never does.
The operating system switch
Google documents two OS-level paths, both noted as working on Android 14 and up. To see the state of each Google app and force a run: Settings → About phone → Google Account → Account sync, then More → Sync now. To turn individual apps on or off: Settings → Passwords, passkeys and autofill → Account sync. On older builds the account list lives elsewhere; rather than guessing, use the search field at the top of the Settings app and search for "Account sync".
After forcing a sync, give it time. Google's own figure is that "it can take up to 15 minutes for Gmail to sync your messages." Declaring a fix failed after ninety seconds is the most common way to end up changing five settings at once and losing track of which one mattered.
Battery and Data Rules That Silence Background Sync
If manual refresh works and automatic delivery does not, sync is enabled and something is preventing it from running while the app is closed. Two device policies do this on Android.
- Background battery usage. Google's Pixel documentation puts this at
Settings → Battery → Battery usage → the app → Allow background usage, with Unrestricted described as removing limits on background battery use and Optimized as the recommended default. The steps are documented for Android 15 and up. If Gmail has been restricted here — sometimes by a battery-saver prompt accepted months ago — background sync becomes unreliable rather than dead, which is why the symptom is intermittent. - Data Saver. At
Settings → Network and internet → Data Saver. Google describes the effect precisely: "This mode lets most apps and services get background data only via Wi-Fi. Currently active apps and services can use mobile data." That produces a phone which receives nothing all day on cellular and then delivers a burst of mail the moment it reaches Wi-Fi. To exempt one app, useData Saver → Unrestricted data. Google notes these steps work on Android 8.0 and up.
That behaviour is almost always misread. The mail is not lost and the app is not broken; the operating system is deferring the fetch until the connection it prefers is available.
iPhone and iPad: Two Different Apps, Two Different Problems
On iOS, "Gmail on the phone" means one of two entirely separate pieces of software, and they fail differently.
The Gmail app for iOS
Google's iOS sync guidance names two checks that do not exist on Android. The first is Apple's own background permission: "On your iPhone or iPad, open the Settings app. Tap General, then Background App Refresh. Scroll to 'Gmail.' Turn on Background App Refresh for Gmail." The second is Gmail's own window: "Tap Menu, then Settings. Under 'General,' tap Data usage, then Sync settings. Set the number of days of email to sync."
Note the shape of the difference. Google's published iOS settings reference does not list a Sync Gmail checkbox at all, and the days-of-mail control sits under General rather than under an individual account. Instructions written for Android will send an iPhone owner looking for a screen that is not there.
Two Apple-side power features override everything above. Low Power Mode, at Settings → Battery → Power Mode on recent iPhones, turns off background app refresh, turns off automatic downloads and turns off email fetch. Low Data Mode, available since iOS 13 at Settings → Cellular → Cellular Data Options for cellular and via the info button beside the network under Settings → Wi-Fi for a specific Wi-Fi network, "turns off Background App Refresh" and stops apps using network data when they are not in the foreground. A phone left in either mode will behave exactly like one with sync disabled.
Apple Mail with a Gmail account
If mail is being read in Apple's Mail app rather than Gmail's, none of Gmail's app settings apply. The relevant control is Settings → Apps → Mail → Mail Accounts → Fetch New Data. Apple documents that with iOS 11 and later, Automatically is the default, and that in this state "your device will fetch new data in the background only when your device is charging and connected to Wi-Fi." Apple also notes that if Push is not offered for an account, it falls back to Fetch.
That single sentence explains a large share of complaints about iPhones being slow to receive Gmail. A phone off the charger and on cellular, set to Automatically, is behaving exactly as designed when it delivers nothing until it is plugged in. Switching to a fixed schedule, or opening Mail manually, changes the outcome immediately.
The Order That Saves Time
The sequence matters more than the individual checks, because several of these settings produce identical symptoms and changing them all at once destroys the diagnosis.
The last resort on Android is the one Google itself labels as such: Settings → Apps → See All Apps → Gmail → Storage and cache → Clear storage, then restart the device. Google warns that this erases drafts, signatures and app settings. It is a genuine fix for a corrupted local database, and a genuine way to lose an unsent draft, so it belongs at the end of the list rather than the start.
What Google Does Not Publish
Several things that get asserted confidently in troubleshooting threads are not documented anywhere official, and guessing at them is how people end up chasing settings that were never the problem.
- The default value of "Days of mail to sync" is not published. Gmail's settings documentation describes the control but states no default and lists no available choices. Read the value on the device rather than assuming it.
- The per-label sync options are not named. Manage labels is documented only as choosing "notification and sync settings for different labels" — the specific options are not listed in Gmail's help.
- There is no published normal delivery latency. The only figure Google states is that a sync can take up to 15 minutes. That is a ceiling for a sync operation, not a promise about how fast a new message reaches a phone.
- A third battery state exists on some devices but is not described in Google's Pixel documentation. That page lists Unrestricted and Optimized under Allow background usage. Manufacturer skins may expose additional restriction levels with behaviour that is not documented by Google, so a phone from another maker may not match the page exactly.
- The bounce timing for an over-quota account is not published. Google states that messages go back to the sender, but not how quickly, and not whether there is a grace period after the limit is crossed.
When This Doesn't Apply
This diagnostic frame assumes a consumer Google Account and the standard Gmail or Mail apps. It breaks down in several situations.
- Managed work or school accounts. A Google Workspace administrator can set policies that override device-side settings, including mail routing rules applied before a message reaches the user's mailbox. If mail from outside the organization is missing entirely and the account is a work address, the sync settings on the phone are not the place to look.
- Third-party mail clients. Outlook, Spark, Thunderbird and similar clients connect over IMAP and have their own sync intervals, folder subscriptions and offline caches. None of the Gmail app paths above exist in them, and a label whose IMAP visibility is switched off in Gmail's settings will not appear at all.
- A sender-side failure. If a specific sender's mail never arrives and no filter matches it, the message may never have been accepted. That is diagnosed from the sender's bounce message, not from the recipient's phone.
- Spam classification. Mail routed to Spam is delivered and synced normally; it is simply not in the inbox. Searching rather than browsing settles this in one step, and it is worth doing before any setting is changed.
- Menu paths on older or heavily skinned Android. The operating system paths cited here are the ones Google documents for Android 14 and 15 on Pixel devices. Other manufacturers rename and relocate these screens, and additional power-management layers may exist that Google does not document.
Every phone-side change here is reversible, which is why the split test comes first: confirming the message is in the web inbox costs twenty seconds and eliminates the three causes no device setting can fix.
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