Blocking keeps spam and unwanted callers away from your team, and capping limits how many calls a destination number receives. This page covers both, and how to handle anonymous callers without losing real leads.

Block spam callers

Note

Methods 1 and 2 (the Blocked Callers list and blocking from the Calls log) work on every plan, Entry included. Method 3 uses the Caller ID Prefix filter, available on the Marketing and Agency plans. Method 4 uses a Greeting and Keypad Entry, available from the Pro plan up.

Nimbata gives you four ways to block unwanted or spam callers. Use whichever method best fits the type of spam you’re dealing with.

Method 1. Block a specific number from the Blocked Callers list

Use this to block a single caller ID you’ve already identified as spam.

  • Go to Call handlingBlocked Callers.
  • Click Add (on an empty list, Add Caller ID to spam).
  • In New Caller ID to Block, enter the caller ID. Optionally tick Delete past calls from this number, or Block number in all projects.
  • Click Add.

The number is now blocked and will appear in your blocked callers list.

Method 2. Block a number directly from the Calls log

Use this when you spot a spam number in your activity log.

  • Go to Activity > Calls.
  • Search for the caller ID in the search bar and select the correct date range.
  • Click the arrow to expand the call details.
  • Click Block (the ban icon). In the confirmation that asks whether to block the number, optionally tick Block number in all projects, then click Yes.

Method 3. Block entire caller ID prefixes using a call flow

Use this to block all calls from a specific area code, country code, or number pattern.

  1. Create a new call flow

    Go to Call handlingCall Flows, click Create, then From Scratch.

  2. Add the Caller ID Prefix filter

    • Click the + button on the canvas, above the Dial step.
    • Select Caller ID Prefix from the Filters menu.

  3. Enter the prefix and route it to Hang up

    • Type the prefix you want to block.
    • The prefix branch keeps the Dial step that was there: click Hang up under Instead in that step.

  4. Route all remaining callers normally

    On the All other prefixes branch, click the + and add a Dial action to your destination number.

Method 4. Use Greeting + Keypad Entry to filter spam naturally

Use this to silently deter robocalls without blocking legitimate callers. Any caller who doesn’t press a key is hung up on, while real callers proceed.

  1. Create a new call flow and add a Greeting

    • Go to Call handlingCall Flows, click Create, then From Scratch.
    • Add a Greeting that instructs callers to press a key to continue. For example, “Press 1 to connect.”

  2. Add the Keypad Entry action

    • Click the + below the Greeting.
    • Select Keypad Entry from the Filters menu.

  3. Route the matching key to Dial, and No match / No input to Hang up

    • On the branch for the correct key press (for example, 1), add a Dial action.
    • Click the + above the Keypad Entry and choose Split for a second branch, type @ in it to make it the No match / No input branch, and add Hang up below it (1).
    Spam filterCall flow is valid. Assign to Tracking Number
    New Call
    Greeting
    Text to speechPress 1 to connect.
    Keypad Entry
    1
    Dial
    Main office(415) 555-0110
    Keypad Entry
    No match / No input
    Hang up
    1
    Callers who press 1 reach the main office; any other key, or no key at all, hangs up (1).

Remove a number from the block list

  • Go to Call handlingBlocked Callers.
  • Select the number.
  • Click the red bin icon and confirm.

Detailed guide: Route by caller location
Detailed guide: Block countries
Detailed guide: Build a keypad menu

Block countries

You can block all calls originating from one or more countries by adding their country code prefixes to a Caller ID Prefix filter in a call flow, then routing those prefixes to Hang up. All other callers continue through the flow normally.

  1. Open the Call Flow Builder

    Go to Call handlingCall Flows and click Create to build a new call flow, or click an existing one to edit it.

  2. Choose how to start (new flows only)

    • Select From Scratch (1), or From Template and the Simple Call Flow template.
    • Either way the flow starts with a Dial step. Keep it: you add the filter above it.
    Create a New Call Flow
    Choose how you’d like to create your call flow
    1From ScratchCreate a completely custom call-flow tailored to your specific needs. Full control over every step and action.
    From TemplateStart with a pre-built template and customize it to your needs. Quick setup with proven call flows.
    Choose From Scratch (1), or From Template.

  3. Add the Caller ID Prefix filter

    • Click the + button on the canvas, above the Dial step.
    • Select Caller ID Prefix from the Filters menu.
    Select a call-flow action✕

    Enhance the call experience with call add-ons and features

    • Add-ons
    • Mask Caller ID
    • Record
    • Greeting
    • Filters
    • Caller ID Prefix1
    • Keypad Entry
    • Day of Week
    • Time of Day
    Click Caller ID Prefix (1) under Filters.

  4. Enter the country codes to block

    Type the country code for each country you want to block, digits only and without the + (for example, 44 for the UK, 49 for Germany), into the prefix branch’s field (1), pressing Enter after each one. A prefix always starts with the country code, can be up to 10 digits, and can’t contain + or other characters (to block a US area code, type 1 and the area code, for example 1312).

    Caller ID Prefix✕
    44✕49✕1
    Each prefix becomes a tag in the field (1).

  5. Route the blocked prefixes to Hang up

    • The branch for the prefixes you entered keeps the Dial step that was there.
    • In that step, click Hang up (1) under Instead.
    Dial✕
    Ring
    DialMultipleSequentialWeightedRound robin
    Instead
    Hang up1Voicemail

    Rings a single destination.

    Destination
    Main office(415) 555-0110
    Receive SMSAlso receive an SMS to your destination when supported by the tracking number.
    Switch the prefix branch's step to Hang up (1).

  6. Route all remaining callers to a destination

    • Click the + on the All other prefixes branch (1).
    • Select Dial and choose the destination number.
    Block countriesCall flow is invalid.
    New Call
    Caller ID Prefix
    44, 49
    Hang up
    Caller ID Prefix
    All other prefixes
    1
    Click the red + (1) under All other prefixes, select Dial and choose your destination.

🎉 Done. Callers from the blocked countries will hear a hang-up immediately, while everyone else connects normally.

Detailed guide: Route by caller location
Detailed guide: Block spam callers
Detailed guide: Assign a call flow

Handle anonymous calls

Anonymous calls present a dilemma: most are spam or robocalls, but some are genuine leads who simply prefer not to share their number. Blocking all anonymous calls is easy, but it costs you those real leads. The best approach is to route anonymous callers to a voicemail that asks them to call back with their number visible. Legitimate prospects will call back; robocalls and spam will not.

Note

Calls from withheld numbers never ring your phone, even without this setup: our telephony carrier doesn’t connect calls that have no caller ID. They still show in your call log and can trigger your email alerts. See Calls from withheld numbers.

  1. Open the Call Flow Builder

    Go to Call handlingCall Flows, click Create, then From Scratch, to create a new call flow.

  2. Add the Caller ID Prefix filter

    • Click the + button on the canvas, above the Dial step.
    • Select Caller ID Prefix from the Filters menu.

    This creates two branches: one for the prefixes you define (1), which keeps the Dial step, and All other prefixes for all remaining callers.

    Anonymous callersCall flow is invalid.
    New Call
    Caller ID Prefix
    Prefix Group
    1
    Dial
    Main office(415) 555-0110
    Caller ID Prefix
    All other prefixes
    The prefix branch (1) still needs its prefix; All other prefixes catches everyone else.

  3. Set one branch to catch anonymous callers

    • In the prefix branch’s field (1), type anonymous.
    • The All other prefixes branch handles all identified callers.
    Caller ID Prefix✕
    anonymous✕1
    Type anonymous into the prefix field (1).

  4. Route anonymous callers to Voicemail

    • On the anonymous branch’s routing step, click Voicemail under Instead.
    • In Voicemail Audio (1), pick a voicemail greeting that asks the caller to call back with their number visible, uploaded on the Voicemails tab of the Media Library. For example, “We’re unable to answer calls from withheld numbers. Please call again with your caller ID enabled.”
    Voicemail✕
    Ring
    DialMultipleSequentialWeightedRound robin
    Instead
    Hang upVoicemail

    Sends callers straight to voicemail.

    Voicemail Audio:
    withheld-numbers.wav1
    Pick the voicemail greeting for anonymous callers (1).

  5. Route all other callers to your destination(s)

    • Click the + below the All other prefixes branch (1).
    • Select Dial and choose the destination number(s) for identified callers.
    Anonymous callersCall flow is invalid.
    New Call
    Caller ID Prefix
    anonymous
    Voicemail
    withheld-numbers.wav
    Caller ID Prefix
    All other prefixes
    1
    Click the red + (1), select Dial and choose the number for identified callers.

🎉 Done. Anonymous callers hear a polite voicemail asking them to call back; genuine leads will, spam won’t.

Detailed guide: Route by caller location
Detailed guide: Block spam callers
Detailed guide: Set up and listen to voicemail
Detailed guide: Assign a call flow

Cap calls per destination

Tip

Call capping is most effective when combined with Sequential, Weighted or Round robin call distribution. See: Ring numbers in order, Split calls by percentage and Take turns between destinations.

Call capping sets a maximum number of answered calls a destination number can take, counted from a start date you choose. Each caller counts once, however many times they call; anonymous callers count on every call. The cap does not reset by itself: once reached, it stays reached until you raise the cap, reset the counter, or turn capping off and on again. Use it to protect agent capacity, control advertising spend, or enforce fair-distribution SLAs.

What happens to a call once its destination reaches the cap depends on the call flow. If the call flow dials only that one number, the call is rejected and ends with the hangup cause Capped. If it routes to several destinations (Multiple, Sequential, Weighted or Round robin routing), the call goes to the next destination, and once every destination is capped, calls are rejected.

Call capping is available on the Marketing and Agency plans; on other plans, Call Capping opens an upgrade prompt. Sequential, Weighted and Round robin routing need the same plans.

  1. Open the Call Capping panel

    • Go to TrackingDestinations.
    • If the Capping column isn’t showing, click Call Capping (1) in the top-right corner. The button disappears once a destination has a cap.

    Destination Numbers

    Where incoming calls are sent when someone dials a tracking number.

    DestinationFriendly NameCall FlowIs Verified
    (415) 555-0110Main officeIn use
    (415) 555-0119Emergency lineIn use
    Click Call Capping (1) to show the Capping column.

  2. Enable call capping for a destination number

    Toggle on the switch (1) next to the destination number(s) you want to cap.

    Tip

    The default cap is 10 calls, counted from today.

    DestinationFriendly NameCapping
    (415) 555-0110Main office0 of 10 callsStart on: 2026-10-141
    (415) 555-0119Emergency line
    Turn on the destination's switch (1). It starts with a cap of 10 calls.

  3. Customize the cap settings

    Click the pencil icon next to the destination, beside “0 of 10 calls”. Its tooltip reads Change Call Capping settings.

  4. Set the call limit and start date

    • In Cap at (1), enter the maximum number of answered calls (1 to 9999).
    • In Start call capping from: (2), pick the date counting starts.
    • Click Apply (3).
    Set the cap (1) and the start date (2), then click Apply (3).

🎉 Call capping is now active. When you build a call flow using a capped destination, Nimbata will display a notice in the builder as a reminder.

Detailed guide: Change the cap
Detailed guide: Ring numbers in order
Detailed guide: Split calls by percentage

Change the cap

Change a cap, or start counting again, from the same Configure Call Capping dialog. A cap never resets by itself, so resetting the counter is how you reopen a destination that has reached its cap.

Tip

You can combine call capping with Sequential, Weighted or Round robin routing to distribute capped calls across your team. See Ring numbers in order, Split calls by percentage and Take turns between destinations.

  1. Open the Call Capping panel

    • Go to TrackingDestinations.
    • If the Capping column isn’t showing, click Call Capping (1) in the top-right corner.

  2. Enable capping for the destination number

    Toggle the Capping switch (2) on for the destination number(s) you want to cap.

    Destination Numbers

    Where incoming calls are sent when someone dials a tracking number.

    DestinationFriendly NameCapping
    (415) 555-0110Main office2
    (415) 555-0119Emergency line
    Call Capping (1) shows the Capping column; turn on a destination's switch (2).

  3. Set the call limit

    • Click the pencil icon next to the destination.
    • In Cap at (1), enter the new maximum number of answered calls.
    • To start counting again, click empty (2) next to calls reached (it shows once at least one call has counted). Moving the start date to a future date also resets the counter.
    • Click Apply (3).
    Enter the new cap (1), reset the count with empty (2) if you need to, then click Apply (3).

🎉 Done. You can return here at any time to change the cap, reset the counter, or turn capping off with the Capping switch.

Detailed guide: Cap calls per destination
Detailed guide: Ring numbers in order
Detailed guide: Split calls by percentage