addy.io Guide: Addy Mail Aliases, Limits & Setup

addy.io is an open-source email alias service: you hand out a throwaway address, it forwards to your real inbox, and you switch that single address off if it leaks. This guide covers the parts of it that are not obvious from the signup page — the two different kinds of alias, the limit that actually constrains the free tier, how replying from an alias works and the two ways it fails, and when a custom domain will collide with your existing mail.

If you are still deciding between services, email alias services compared puts addy.io next to SimpleLogin and Firefox Relay on price and capability. This page assumes you have picked addy.io, or are close to it.

The naming, because it confuses everyone

The service launched as AnonAddy and renamed to addy.io. Both names still appear in the product: the source lives at github.com/anonaddy/anonaddy, the shared alias domains include anonaddy.com and anonaddy.me alongside addy.io, forwarded mail carries an X-AnonAddy-Authentication-Results header, and your personal subdomain is offered as username.addy.io while the FAQ still documents the legacy username.anonaddy.com form, which continues to work.

So AnonAddy, anon addy, addy mail and addy.io all refer to the same service. It is run by a UK developer, Will Browning. The mail server sits in Amsterdam with Greenhost, and the backup mail server is in Warsaw with UpCloud — so the relay is EU-hosted, but the operator is in the UK, which is the jurisdiction split to weigh if that matters to you.

The two alias types, and why the difference decides everything

This is the single concept that determines whether addy.io suits you.

Standard aliases live on a subdomain that belongs to you: anything@yourname.addy.io. You pick the username once. After that, every address on that subdomain works as a catch-all — you invent groupon@yourname.addy.io at the checkout page, and addy.io adds it to your dashboard when the first message arrives. You never pre-create anything. These are unlimited on every plan, including free.

Shared-domain aliases use addy.io’s own domains, in generated forms like x481n904@anonaddy.me, with options for random characters, random words, random nouns or random names. These are capped by plan.

The tradeoff runs in one direction. Standard aliases are effortless and unlimited, but every site you sign up to sees the same yourname.addy.io subdomain — which does not reveal your real address, but does let two services comparing notes see one account behind both aliases. Shared-domain aliases carry no such fingerprint, which is exactly why they are the metered resource.

Two ways to soften this. Additional usernames split aliases into separate subdomains — personal, work, hobbies — so a leak in one compartment does not link to another. A custom domain removes the problem entirely, at which point nobody can tell your addresses are aliases at all.

If linkability is a new idea, what email metadata leaks is the fuller version of why a shared identifier across accounts matters even when the content is private.

Plans and the numbers that actually bind

Taken from addy.io’s published pricing, retrieved August 2026:

	Free	Lite	Pro
Price	$0	$1/mo billed yearly	$3/mo billed yearly, $4 monthly
Standard aliases	Unlimited	Unlimited	Unlimited
Active shared-domain aliases	10	50	Unlimited
Recipients (real inboxes)	1	5	30
Available alias domains	2	6	7
Custom domains	None	1	20
Additional usernames	None	5	20
Rules	None	5	20
Anonymous reply/send per day	None	50	200
Monthly bandwidth	10 MB	100 MB	Unlimited
Failed-delivery replay, priority queue, regex auto-creation	No	Yes	Yes
Blocklist	No	No	Yes

Duo ($4.50/mo billed yearly, two members) and Family ($7.50/mo billed yearly, five members) give every member full Pro on an independent account under one subscription, with the option to share a custom domain across the group. The arithmetic decides it: Duo beats two separate Pro seats ($4.50 against $6), and Family beats three ($7.50 against $9). For two people it is Duo, not Family.

Note the one feature that is genuinely Pro-only rather than merely paid: the sender blocklist. Lite gets failed-delivery replay, the priority queue, regex auto-creation and the option to disable catch-all, but blocking a sender outright is on Pro.

Bandwidth is the real free-tier ceiling

Alias count gets the marketing; bandwidth is what stops people. Every forwarded message and every reply increments a byte counter that resets at the start of the calendar month.

addy.io’s FAQ does the arithmetic in public: it puts the average email at roughly 75 KB, which makes the free plan’s 10 MB about 140 forwarded emails per month, and Lite’s 100 MB roughly 1,400. Attachments count, and the maximum message size is 25 MB including them. Mail blocked because an alias is inactive or deleted does not count.

Two consequences. Image-heavy newsletters and attachments burn the allowance far faster than the 140-message figure suggests, so if aliases are where your newsletters land, budget for Lite from the start. And deactivating a spam-hit alias stops the bandwidth drain immediately, because discarded mail is not counted.

Alias creation is separately rate-limited: 10 per hour on Free, 20 on Lite, 50 on Pro, with excess deferred rather than lost. This only bites during a bulk migration.

Replying and sending from an alias

Receiving through an alias is the easy half. The feature that makes aliases usable for real correspondence is sending out through one, so the recipient only ever sees the alias — otherwise your real address leaks the moment you hit reply.

The mechanism is simple: you reply to the forwarded message from a verified recipient address on your account, addy.io rewrites the sender, and the other party sees the alias. The “This email was sent to…” banner addy.io adds to forwarded mail is stripped automatically from your reply, so long as you have not edited it. Attached OpenPGP public keys and signatures are also removed on the way out, because a PGP key usually carries your real address as its identity.

Note the plan gate: anonymous reply and send is a paid feature, capped at 50 per day on Lite and 200 on Pro. There is also no SMTP option — you cannot point a mail client at an alias with credentials and send directly. Replies go through the forwarding path or not at all.

Two failure modes are worth knowing before they happen, because both look like the service is broken.

The reply comes back to you instead of going out. This means you sent from an address that is not a verified recipient on your addy.io account. From addy.io’s perspective you are just another sender writing to the alias, so it forwards the message to you as normal. Check the “from” address in your sent items — this bites people with multiple identities in one mail client.

The send is rejected, or you get an “Attempted reply/send from alias has failed” notice. Sending from an alias triggers anti-spoofing checks, and your verified recipient’s domain has to pass DMARC for addy.io to be confident the request really came from you. Mailbox providers like Gmail, Outlook, Proton Mail, Tuta and Mailbox.org already publish DMARC, so this never affects them. It affects people whose recipient address is on their own domain without a DMARC record. The fix is a TXT record at _dmarc with a policy such as v=DMARC1; p=quarantine; adkim=s, on top of working SPF and DKIM. Setting up a custom domain with an encrypted mail provider covers those three records in detail.

A separate rejection, 550 5.1.1 Recipient address rejected, means the alias was deleted or never existed and catch-all is off. Restore or create it first.

PGP forwarding: the feature most alias users skip

By default an alias service can read the mail it relays. That is inherent to forwarding, and it is the trust you accept when you use one.

addy.io lets you close that gap by adding an OpenPGP public key per recipient. Forwarded mail is then encrypted to your key before delivery, attachments included, and you can optionally have subject lines replaced as well — worth doing, since the subject is otherwise the most revealing thing left in clear text. Encrypted forwards are signed with addy.io’s no-reply@addy.io key, whose fingerprint is published in the FAQ and whose public key is on keys.openpgp.org, so you can verify a message came from the relay rather than from someone spoofing it.

Unlike SimpleLogin, which reserves PGP forwarding for its paid tier, addy.io offers it on every plan. If you do not yet have a key pair, how to set up PGP email encryption covers generating one; you only need the public half here. Mail is stored only on a failed delivery, and only if you enable that option, so the exposure window is the relay itself rather than an archive.

Custom domains, and the MX collision to avoid

A custom domain gives you anything@yourdomain.com aliases with no visible tell, and it makes the whole arrangement portable: switch alias services later and every address keeps working. Lite includes one domain, Pro includes twenty.

The trap is DNS. Incoming mail follows a domain’s MX records, and one domain publishes one set of them, so you cannot point a domain at addy.io while it is also delivering your mailbox at Proton Mail, Namecheap or anywhere else. Adding addy.io’s MX records replaces your provider’s rather than sitting alongside them. addy.io’s own recommendation is to either migrate the domain fully, or add a subdomain — alias.yourdomain.com — to addy.io and leave the parent domain with your mail provider. The subdomain route is the right answer for almost everyone, because it lets one domain do both jobs.

Catch-all is on by default for custom domains, which is what makes invent-on-the-spot addresses work. That also means unfamiliar aliases will appear in your dashboard when spammers guess addresses at your domain — normal behaviour, not a sign of compromise. The option to disable catch-all is a paid feature.

Self-hosting and the API

The full application is open source and self-hostable, so the relay you are trusting with your mail can be one you run. The mobile apps and browser extension are open source too, and free against either the hosted service or your own instance. A developer API covers aliases, recipients, domains and additional usernames, driven by a key you create in account settings — the hook if you want a script to mint an alias at the moment it provisions an account.

A sensible setup order

1. Pick a username you have never used elsewhere. It becomes the visible half of every standard alias, so a username tied to your real name defeats the point.
2. Verify your real inbox as a recipient — ideally an encrypted mailbox rather than the one you are trying to protect.
3. Install the browser extension. Aliasing only sticks as a habit when generating an address takes one click at the signup form.
4. Add your OpenPGP public key to the recipient, and turn on subject replacement.
5. Name aliases after where they are used, so a spam surge tells you immediately which company leaked or sold you. That is the whole payoff, and why your email ends up on data broker lists explains what you are catching.
6. Add a custom domain, or a subdomain, once you are past the trial stage — and check the MX conflict above first.

For the service-agnostic version of the per-signup workflow, including how to keep a small number of stable aliases you never burn, see how to set up email aliases. If a red spoofing banner ever shows up on a forwarded message, how to read email headers explains how to read the X-AnonAddy-Authentication-Results header that says why.

When addy.io is the wrong answer

If you already pay for Proton, SimpleLogin is bundled into that ecosystem and integrates more tightly. If you need more than the 20 custom domains addy.io Pro allows, SimpleLogin’s pricing puts unlimited domains and unlimited mailboxes on one $4/month tier, at the cost of a $1/month premium over Pro and no free-tier equivalent. If five addresses is genuinely all you will ever need, Firefox Relay’s free tier hands you five permanent masks and nothing to configure.

And no alias service is encrypted email. Aliases protect the address; end-to-end encryption protects the message. The two compose well — the find-your-setup wizard puts a provider and an alias strategy into one plan rather than making you pick them separately.