Klaviyo is a marketing automation platform built for email and SMS. Connecting it to LettrLabs lets you trigger personalized, robotically handwritten cards and printed postcards whenever a customer lands in one of your Klaviyo segments — so direct mail becomes another channel in your existing lifecycle marketing, right alongside email and SMS.
This guide walks through connecting your Klaviyo account, building your first automation, and understanding how a Klaviyo segment actually turns into a mailed card.
Before you start
A Klaviyo account (a free account works — you can create one during setup if you don't already have one).
At least one segment in Klaviyo. LettrLabs triggers off segment membership, not static lists — lists don't appear as an option because they don't track when someone was added.
A LettrLabs card template you want to send, or plan to create one during setup.
Step 1: Connect your Klaviyo account
From your LettrLabs dashboard, open the Automations area and go to Manage Integrations.
Find the Klaviyo card and open it. This opens the Klaviyo Integration panel.
Click Setup Now. LettrLabs generates a secure authorization request and sends you to Klaviyo's own login/authorization page.
Log in to your Klaviyo account (or create one — it's free to get started).
Klaviyo will show you the permissions LettrLabs is requesting — read access to your accounts, lists, segments, and profiles, plus webhook access. Review and approve the connection.
Klaviyo redirects you back to LettrLabs automatically. Your integration now shows as connected, and you're ready to build an automation.
Note: if you close the window or deny access partway through, nothing is connected — you can simply click Setup Now again to retry.
Step 2: Create your first Klaviyo automation
Click New Automation (or Create New Automation if this is your first one), choose Klaviyo as the source, and give it a name you'll recognize later.
Choose a card template — a design you've already created, or double-click the create option to design a new one. You can reuse a design from a past order as a template too.
Select the Segment you want to mail to. This list is pulled live from your Klaviyo account. Choosing a segment means: whenever a new profile joins that segment, LettrLabs will consider them for a mailing.
Optionally, add profile filters to narrow the segment further before a card gets sent.
AND — every condition in the group must match.
OR — any one condition in the group is enough to match.
Set your Monthly Sending Limit — the maximum number of cards this automation will send per month (minimum 50) — so spend stays predictable as your segment grows.
Choose a postage type, and attach a coupon or discount code list if this campaign uses one.
If you're on a plan that includes it, you can enable Holdout Testing (available for Klaviyo, Shopify, and Lead Reveal automations) — set a holdout percentage between 25–50% to hold back a control group of otherwise-qualifying profiles, so you can measure the incremental impact of the mailer against a group that didn't receive one.
Click Save.
Step 3: Test before you go live
A newly saved automation starts in Testing status rather than mailing immediately. During this window (roughly five days), you can add people to your Klaviyo segment to confirm they're picked up correctly by the automation — nobody added while in Testing status is actually mailed. This is your chance to validate the segment and filters are catching the right people before spending on postage.
Step 4: Activate your automation
Once you've confirmed everything looks right, open the automation and change its status to Active. From this point on, profiles who join your selected segment and match your filters will be mailed according to your template, postage, and monthly limit settings. You can switch an automation to Inactive at any time to pause it, and back to Active to resume it.
How the trigger actually works
It's worth understanding what happens behind the scenes, since it isn't instantaneous:
LettrLabs runs a recurring daily check against Klaviyo's segment membership for each active automation, looking for profiles added to the segment since the last check.
Each matching profile is run through any profile filters you configured.
Profiles that pass are address-verified and sanitized, checked for duplicates and do-not-mail/suppression rules, and then queued as a mail order.
Because this is a scheduled check rather than an instant, real-time webhook, there can be a short delay (typically up to a day) between someone joining your Klaviyo segment and their card being queued for mail. Plan your segment timing with that in mind — for example, a "30 days since last open" segment will naturally pick up new qualifying profiles once per day, not the instant they cross the threshold.
Disconnecting Klaviyo (revoke access)
Open the LettrLabs app and go to Automations > Manage Integrations.
Open the Klaviyo integration and choose Revoke.
Confirm the revoke. This deauthorizes LettrLabs' access on Klaviyo's side and automatically deactivates any Klaviyo automations tied to that connection.
To reconnect later, simply repeat the Setup steps above — your existing automations and templates aren't deleted, just paused until you reconnect and reactivate them.