FAQ
Frequently asked questions
Everything you need to know about email sub-addressing and how Subaddressify works.
What is email sub-addressing?
Email sub-addressing (also called plus addressing or tagged addressing) is a technique that lets you create variations of your email address by appending a + and a tag. For example, if your address is you@gmail.com, you can use you+tag@gmail.com. Emails sent to any variation arrive in the same inbox. It's defined in RFC 5233 and supported by most modern email providers.
Does sub-addressing work with my email provider?
Sub-addressing using the + symbol is supported by Gmail, Outlook, ProtonMail, Fastmail, and Hey. iCloud Mail and Yahoo Mail do not support it. A small number of websites may also incorrectly reject email addresses containing a + character — in those cases, use your base address directly.
Will using a sub-address prevent spam?
Sub-addressing doesn't prevent spam outright, but it lets you identify exactly where spam came from and filter it automatically. If you signed up to example.com with you+2026-01-01-example-com@yourdomain.com and start receiving spam there, you know example.com shared or leaked your address. You can then create a filter to automatically delete or archive anything sent to that sub-address.
Is my base email address safe?
Yes. Your base email is stored using Chrome's built-in sync storage (chrome.storage.sync) — it lives in your browser profile and is never transmitted to any external server. Sub-addresses are computed locally using the current hostname and date; nothing is logged or recorded by the extension.
Can I use this with Gmail?
Yes. Gmail natively supports sub-addressing. Emails sent to you+tag@gmail.com arrive in your main Gmail inbox. To organise them, create a Gmail filter using the "To" field: set it to match your sub-address (e.g. to:you+example-com), then choose an action like "Apply label" or "Skip the inbox".
What if a website doesn't accept + in email addresses?
Some websites incorrectly validate email addresses and reject the + character, even though it is perfectly valid per RFC 5322. In those cases, use your base email directly. The extension won't cause any issues — simply don't use the generated address for that site. This is unfortunately a bug in the website's validation, not a limitation of sub-addressing.
Do I need to create a new email account?
No. Sub-addressing works with your existing email address. All emails to any sub-address arrive in the same inbox. No new accounts, no forwarding rules needed at the provider level. You only need filters if you want to automatically sort incoming mail.
How do I set up filters to sort emails by sub-address?
In Gmail: go to Settings → Filters and Blocked Addresses → Create a new filter. In the "To" field, enter your sub-address (e.g. you+example-com@gmail.com). Choose an action — apply a label, skip the inbox, delete, or forward. In Outlook: go to Settings → Mail → Rules → Add new rule, then filter by "Recipient address contains" your sub-address.
Can I tell who leaked or sold my email?
Yes — that's one of the most powerful uses of sub-addressing. Because each sub-address is tied to a specific website and date (e.g. you+2026-01-15-retailer-com@yourdomain.com), any spam arriving at that address tells you exactly which site your email came from and approximately when it was shared. This works for data breaches too.
Does the extension store which sites I visit?
No. The extension reads the current page hostname only when you open the popup — it is not monitoring your browsing in the background. The hostname is used immediately to generate the sub-address and is not stored or logged anywhere.
Can I customise the format of the generated address?
The current format is fixed: localpart+DATE-HOSTNAME@domain.com. This standardised format makes it easy to build consistent filters and keeps things simple. Custom format support may be added in a future release — follow the GitHub repository for updates.
Is Subaddressify free?
Yes, completely free. There are no paid tiers, no subscriptions, and no premium features. The extension is also open source, so you can inspect the code, fork it, or contribute improvements.
Still have questions?
Open an issue on GitHub →