Audience

Topics

Subscription categories within a sending domain. Contacts choose which topics they receive; a campaign can target a single topic.

A topic is a category of mail within one of your sending domains — for example “Product updates” or “Weekly newsletter”. Topics give your contacts finer-grained control: a contact can opt out of one kind of email on a hosted preference page instead of unsubscribing from everything you send. A contact can belong to multiple topics.

Topics are the more deliverability-friendly alternative to all-or-nothing unsubscribes: letting a contact drop a single topic keeps them on your list for the mail they still want. They differ from segments — segments are your private filters for organizing contacts, while topics are user-facing preferences your contacts manage themselves.

Default subscription: opt-in vs opt-out

When you create a topic you choose its default subscription — how contacts start out relative to it:

Default	Behavior
Opt-in	Every contact receives this topic unless they have explicitly unsubscribed from it.
Opt-out	No contact receives this topic unless they have explicitly subscribed to it.

The default subscription is fixed at creation and cannot be changed later. Pick it carefully — to switch a topic between opt-in and opt-out you would have to create a new topic.

Visibility: public vs private

Each topic also has a visibility that controls whether it appears on the contact’s preference page:

Visibility	Who sees it on the preference page
Public	All contacts can see and toggle the topic.
Private	Only contacts who are already opted in to the topic can see it.

Unlike the default subscription, a topic’s name, description, and visibility can be edited after creation.

How topics affect sending

A campaign may target a single topic via topic_id.
So may a single send: `POST /emails` accepts topic_id too.
When either does, the send skips any recipient who is not subscribed to that topic (per its opt-in/opt-out default and the recipient’s own choices) — on top of the audience-wide unsubscribe and the account suppression list.
Topics never override compliance: a contact who unsubscribed from the whole audience is never emailed, regardless of topic.

A topic send always carries an opt-out

Setting topic_id marks a send as subscription mail, so MailBlastr gives every recipient a way to leave — the same two mechanisms a campaign gets, added automatically:

an unsubscribe footer in the HTML body (skipped if your body already carries a MailBlastr unsubscribe link, e.g. via the {{{MAILBLASTR_UNSUBSCRIBE_URL}}} merge tag), and
an RFC 8058 `List-Unsubscribe` header with `List-Unsubscribe-Post` for native one-click unsubscribe.

The link is minted per recipient, so each to/cc/bcc address receives its own copy with only its own opt-out link. The recipient does not need to be a contact — a topic opt-out can be recorded against a bare email address, which is what makes topic_id safe to use for mail sent to addresses that are not on your list.

The scope of the opt-out is that one topic — never a global unsubscribe. The address keeps receiving your other topics, your campaigns, and your transactional mail; only later sends carrying the same topic_id skip it. Conversely, a send without a topic_id is transactional and carries no unsubscribe footer or header at all: an unsubscribe writes a suppression that blocks every later send to the address, so MailBlastr never puts one on a receipt or a password reset. See Unsubscribe links.

Both kinds of opt-out are listed together in the dashboard under Audiences → Topics → View opt-outs: contacts who turned the topic off on their preference page, and email addresses that used the unsubscribe link on a topic send.

The audience-wide Subscribed status is the master switch. If a contact’s global unsubscribed flag is true, they receive nothing — even from a topic they are opted in to. Only when the global status is subscribed do per-topic subscriptions decide what they receive. See Managing unsubscribed contacts.

The preference page

Each per-contact unsubscribe link resolves to a hosted preference page where the contact can:

unsubscribe from one or more individual topics (and keep receiving the rest), or
unsubscribe from everything you send (this flips their global unsubscribed flag and stops all campaigns).

The page lists every public topic; private topics appear only for contacts already opted in to them. Include the link in a campaign with the {{{MAILBLASTR_UNSUBSCRIBE_URL}}} merge tag.

The unsubscribe link on a topic send is different: it names the topic being left and offers only that choice — no “unsubscribe from everything” box — because a topic link is not consent to stop the sender’s account and transactional mail.