The A2P 10DLC compliance guide covers the basics of opt-outs. This one goes deeper: every keyword K3X handles automatically, the do-not-message list you control, the quiet-hours config that prevents 3am sends, and the audit trail you need for TCPA defense.
STOP keywords (handled automatically by K3X).
When an inbound SMS to your number contains any of these as the only word (case-insensitive), K3X marks the sender as opted-out and blocks all future outbound SMS to them from any of your numbers:
STOP
STOPALL
UNSUBSCRIBE
CANCEL
END
QUIT
OPTOUT
K3X automatically sends a confirmation reply: "You've been unsubscribed from K3X messages. No more messages will be sent. Reply START to opt back in." This is required by carriers — not optional, not configurable.
The opt-out is org-wide, not per-number. If a lead replies STOP to your sales rep's number, they're opted out of your support number too. This is also a carrier requirement; carriers expect a single opt-out to cover your entire sending entity.
START keywords (re-opt-in).
To rejoin, a recipient texts one of these to any of your numbers:
START
YES
UNSTOP
OPTIN
K3X removes them from the opt-out list and sends: "You've been resubscribed to K3X messages." Their next inbound message after that goes through normally.
HELP keyword.
When a recipient texts HELP or INFO, K3X auto-replies with: "K3X support: reply STOP to unsubscribe, or contact [email protected] for help. Msg & data rates may apply."
Configurable under Settings → Compliance → SMS Auto-replies → HELP response. Keep it under 160 characters so it fits in one SMS segment. Carriers expect this response — disabling it isn't recommended (and may trigger a compliance flag on your account).
Your own do-not-contact list.
Separate from the carrier opt-out list, K3X has a Do Not Contact list you control. Use it when someone asks not to be contacted verbally, by email, or through another channel — not just SMS.
Add from any lead's profile menu → Do Not Contact. Pick which channels to block:
SMS — same effect as a STOP reply.
Calls — outbound calls to this contact are blocked from the dialer with a warning. Also disables Agent-initiated calls.
Email — outbound emails to this contact are blocked.
All channels — enables all of the above.
Reps trying to contact a DNC lead see a banner explaining why, with a one-click link to remove the block (admin-only) if it was set in error.
Quiet hours.
The TCPA prohibits commercial telemarketing calls or texts to consumers outside 8am–9pm in the recipient's local time zone. K3X enforces this automatically for any number with Quiet hours enabled (default: on for new numbers).
Configure under Settings → Phone Numbers → [number] → Quiet hours:
Start / End hour — defaults to 9am / 8pm to give yourself a one-hour buffer on each side.
Timezone source — Recipient's local time (recommended) or Your business timezone.
Days — typically Monday–Saturday; many teams exclude Sunday.
What happens when you try to send during quiet hours?
Manual sends get a warning dialog: "This message would arrive at 10:43pm in the recipient's time zone. Send anyway, or queue for 9am tomorrow?" You pick.
Agent sends are auto-queued for the next allowed window without prompting.
Replies to inbound messages bypass quiet hours — if someone texts you at 11pm, you can text back.
Where the recipient's time zone comes from.
K3X looks up the area code's geographic region and uses its dominant time zone. This is approximate — area codes don't always match where someone actually lives. For more accuracy:
If the lead has an explicit timezone field set, K3X uses that.
If they have an address, K3X uses the city's time zone.
Otherwise, area code.
You can override per-lead from their profile if you know they've moved.
The audit trail.
Every opt-out event is logged with a timestamp, the inbound message that triggered it, and which K3X user's number received the request. View under Settings → Compliance → Opt-out history.
If you're ever served with a TCPA complaint, this log is your primary defense. Export to CSV from the same page — keep it in your legal hold workflow.
What you can't override.
STOP responses. No admin can override an opt-out via the UI. The recipient must text START. (You can theoretically re-add their number with consent documented, but if you do this without their explicit re-opt-in, you're risking complaints.)
The auto-reply to STOP and HELP. Required by carriers. Disabling these can get your messaging suspended.
Quiet hours on calls in some states. Texas, California, and a few others have stricter time-of-day rules than federal TCPA. K3X uses the most restrictive of (federal, state) when both apply.
Next: MMS — sending images, PDFs, and other media →
