What is plus-addressing and tagging?

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You've probably seen an email address like captain+newsletter@tidalmail.com. That little plus sign and tag is called plus-addressing (or sometimes email tagging). It's a built-in trick that lets you create instant variations of your email address without setting up anything new.

But Here's how it works: captain+newsletter@tidalmail.com routes to the same inbox as captain@tidalmail.com. The mail server ignores the "+newsletter" part for delivery, but the tag stays visible in the headers and "To" field. This means you can create an unlimited number of tagged versions of your address and use them to track where mail comes from or filter messages automatically.

Common uses: signing up for newsletters (you+amazon@domain.com, you+ebay@domain.com), creating throwaway addresses for sketchy websites, tracking which signup forms leak your address to spammers, or setting up inbox filters. If you start getting spam sent to you+storeX@domain.com, you know exactly where it came from.

The main frustration: poorly written web forms reject plus signs as "invalid" even though they've been allowed since RFC 822 in 1982. If you run a signup form, don't block the plus sign. If you're a user and a form rejects your tagged address, that's the form's bug, not yours.

Plus-addressing is the most common flavor of sub-addressing, but different providers use different symbols. Gmail and most others support the plus sign. Some older systems use hyphens or underscores instead. The concept is the same: one mailbox, many variations.

For senders, be aware that some users create tagged addresses to track you. If a subscriber signed up as user+yourcompany@domain.com, they're probably watching how you use their address. Don't be shady with it, and don't strip the tag when you send mail back to them (some ESPs do this automatically, which breaks reply threading). Want to test if your mail server supports plus-addressing? Send an email to yourself with a "+test" tag and see if it arrives. Most modern providers support it out of the box.

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I read this on the Email Almanac about plus-addressing: "Plus-addressing lets you add a '+tag' to your email address (like captain+newsletter@tidalmail.com) to create instant variations that route to the same inbox. It's useful for tracking signups, filtering mail, and catching spam leaks. Most modern providers support it, but some web forms incorrectly reject it." Help me apply this to my situation: 1. If I'm a SUBSCRIBER: How do I use plus-addressing to protect my inbox and track who's leaking my address? 2. If I'm a SENDER: Should I strip tags from subscriber addresses, or leave them intact? What breaks if I remove them? 3. If I run a SIGNUP FORM: How do I make sure my form accepts plus signs (and other valid special characters)? 4. Deliverability impact: Does sending to tagged addresses affect my sender reputation or deliverability? --- My context (fill in what applies): - Role: subscriber / sender / developer - Platform: [Gmail, Outlook, custom domain, or ESP like Mailchimp/SendGrid] - Use case: [tracking signups, filtering newsletters, building a form, analyzing engagement] - Current challenge: describe what you're stuck on

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