How much data does email use?

Where an inbox spends its data

• The text of each message, which is tiny next to anything else on your phone.
• Images in newsletters and promotions, loaded from the sender's servers when you open the message.
• Attachments, from a one-page PDF ticket to a video.
• Sync, meaning the folders and older messages the app keeps up to date.

No email service publishes a data figure, because every inbox is different. A day of short replies costs next to nothing; one forwarded video costs more than a week of them. That is why the useful settings are not about email in general but about when the phone checks for mail, what it downloads by itself and how much old mail it keeps.

Push, Fetch and Manually on iPhone

In Settings, Apps, Mail, Mail Accounts, Fetch New Data sets how the Mail app receives messages. Apple explains that the default depends on what your email service provides: with Push, new mail arrives as it is sent; if Push is not available, the account uses Fetch, which checks on a schedule or when you open Mail. Automatically is the default, and with it the iPhone only fetches in the background while it is charging and on Wi-Fi.

For a trip, any of these is fine, since checking for new messages is light. Choose Manually if you want Mail to update only when you open it. If you would rather Mail never touched the travel line, go to Settings, Cellular and turn it off in the list of apps; Apple says the app then uses only Wi-Fi.

Gmail on Android: the attachment setting already helps

Open Gmail, tap Menu, then Settings and your account. Four settings matter. Download attachments, when on, only downloads attachments automatically on Wi-Fi; on mobile data you download them yourself by tapping. Days of mail to sync sets how many days of mail are kept on the phone and available offline, so a smaller number means less to keep in sync. Sync Gmail, when off, stops new mail arriving on its own until you pull down to refresh. Images decides whether pictures show inside your messages.

Google notes that some of these apply per account, so if you have a work account and a personal one in the same app, check both. Turning off Images is the one that makes newsletters lighter, at the cost of a plainer inbox.

Large attachments usually arrive as links

The biggest files rarely travel inside the email. Personal Gmail accounts have a 25 MB attachment limit, and above it Gmail removes the file and adds it as a Google Drive link instead. Apple's Mail Drop works the same way through iCloud: it sends attachments up to 5 GB as a download link, which the recipient has 30 days to use, and Mail offers it when a message is bigger than your provider's limit.

On a trip that works in your favour. When a cousin sends the 300 MB video from the wedding you missed, what lands in your inbox is a link, and nothing big is downloaded until you tap it. Leave those links for the hotel Wi-Fi. The same goes for the shared photo albums and cloud folders that arrive by email after group trips.

The morning check-in email, and what to save

The attachments you actually need on a trip are small and important: the hotel confirmation, the boarding pass, the museum tickets, the car hire voucher. Open them once on Wi-Fi and save them where you can reach them without a connection. In Mail on an iPhone, touch and hold the attachment and choose Save to Files, or Save Image for pictures. To find them all, turn on the filter in a mailbox, tap Filtered by and turn on Only Mail with Attachments.

Boarding passes do better in the wallet app than in an inbox; this guide explains how they behave offline, and this one covers the rest of your documents.

Codes by email keep working on a data-only line

Email has one quiet advantage abroad: it only needs a data connection. A verification code sent by email arrives on a travel eSIM just as it would at home, while a code sent by SMS goes to your home number. Snoozim's eSIMs are data-only, with no number for calls or SMS, so where a service lets you choose, email or an authenticator app is the easier route. The guide to two-factor authentication covers the options, and this one explains how to keep receiving bank SMS codes on your home line.