Gmail Aliases and the Plus-Sign Trick: A Free Temp-Mail Alternative

How the plus-sign trick works

Gmail treats the local part of an address (the text before the "@") as the username and ignores anything after a "+" for routing purposes. So janedoe+school@gmail.com, janedoe+notes@gmail.com, and janedoe+important.emails@gmail.com all land in the same janedoe@gmail.com inbox. Google's help documentation uses those exact examples to illustrate how tags work.

The address you give out is technically unique per tag, which means you can build a Gmail filter that watches for mail arriving at a specific tagged version and applies a label, skips the inbox, or archives it automatically. The sender sees the full tagged address in their records, so if you signed up for a newsletter with janedoe+deals@gmail.com and you start receiving unrelated marketing, the tag tells you who shared or sold the address.

What it is good for

The two most practical uses are filtering and tracing.

For filtering, you assign a tag per category or sender type at the point of signup. Everything from e-commerce goes to yourname+shop@gmail.com, newsletters to yourname+news@gmail.com, and so on. A single Gmail filter per tag then routes the mail where you want it, automatically, without any manual sorting.

For tracing, the tag is a breadcrumb. If yourname+signup@gmail.com starts receiving mail from parties you never gave that address to, you know the site you used it on either shared the list or was breached. Privacy Guides notes that dedicated aliasing services exist specifically for this purpose and offer stronger protections than plus addressing, but for casual tracing the Gmail tag is free and takes no setup beyond typing it in.

Both uses work best for low-stakes signups where you have some trust in the recipient but want to stay organised, and where you do not particularly need to hide that the address belongs to a Gmail account.

Where it falls short

The base address is always exposed. A tagged address like janedoe+coupon@gmail.com reveals janedoe@gmail.com to anyone who looks at it. Stripping the "+coupon" part takes a regular expression that any developer can write in a line. Privacy Guides describes this directly: sites and trackers can trivially remove anything after the "+" sign to recover the underlying address. So the privacy benefit of a tagged address is slim; you are organising mail, not hiding your identity.

Some sites compound the problem by rejecting plus-sign addresses outright. Input validation that refuses the "+" character is common enough that you may find the trick fails before you ever see a confirmation email. There is no workaround in that case short of using a different address.

The comparison to a catch-all alias on a custom domain illustrates the gap. A Fastmail catch-all configuration, for example, routes any address at your own domain to a single inbox, so janedoe@yourdomain.com, shopping@yourdomain.com, and any other variant all land together, with no central address for a third party to infer. The alias is the address; there is no base to strip to. Gmail plus addressing uses a shared public domain (gmail.com) with a recoverable base, which is a structurally different thing.

Plus-tag vs real alias vs temp mail

These three tools sit on a spectrum that runs from convenience to separation.

A Gmail plus tag is the lowest-effort option and stays inside your existing inbox. It is good for sorting and for tracing which of your trusted signups shared your address. The base address is visible to recipients, the tag is strippable, and some sites will block it.

A real alias from a dedicated aliasing service (or from a catch-all on a custom domain) gives you an address that differs from your base address, so neither the recipient nor a data broker can easily recover the real one. These services vary in cost and configuration, and the trade-offs between them and temporary mail are covered in full in the comparison post.

A disposable address from a service like TempMailSpot takes the separation further still: the address is not your domain at all, it does not exist permanently, and it can be discarded without touching your inbox or any credentials. There is no "base address" to recover because there was never a connection to your real email. That is the right fit for one-time signups where you do not want the interaction anywhere near your inbox, even a filtered corner of it.

The question is what you are trying to accomplish. If you want to stay organised and trace which of your trusted correspondents sells lists, a Gmail plus tag is a free answer. If you want to give a site an email that cannot be traced back to you, only a disposable or properly isolated alias does that job.