How to warm-up an SMS sending number

15 minute read

Why do I need to warm-up an SMS sending number?

When you lease a new number for your SMS marketing, or move from another provider, you need to warm-up your sending number reputation to ensure you avoid carrier violations. Warming-up your sending reputation is the process of re-introducing the new number to your recipients and establishing a positive reputation with the carriers.

Cold texting, sending text messages to non-opted in recipients, is illegal.

Consider your sending number

First, it’s important to understand that in SMS text messaging, there are different types of sending numbers:

Type of NumberDescription
Short CodeA short code is a 5- to 6-digit number used to send SMS or MMS messages.
Toll-freeA toll-free number, in the United States, is a special 10-digit number that usually starts with an 8 (800, 888, 877, 866, etc.).
10 Digit Long Code (unregistered)A long code is a standard, 10-digit number that also can be used to send SMS or MMS messages. Unlike a toll-free number, the long code is associated with a specific regional area code.
10 Digit Long Code (registered)A long code that has been 10DLC registered.

While it is important to warm-up your sending number, it is most relevant for toll-free and long codes.

Key differences between short codes and long codes

Short codes, toll-free, and registered 10 digit long codes are all numbers that have been registered and vetted by the carriers.

However, this does not mean that you can ignore your sending number reputation.

What is sending number reputation?

When you send SMS marketing or transactional text messages the carriers (AT&T, T-Mobile, Verizon and others) monitor your traffic and content. They are constantly looking for abuse or for content that should be blocked. When content is blocked it is known as a carrier violation. And when a carrier violation occurs, it can be detrimental to your entire SMS marketing campaign.

The monitoring of your traffic and content creates a reputation associated with the sending number.

What do carriers consider as part of sending number reputation?

There are many factors that determine your sending number reputation. Some of which include:

  • Number registration – is the sending number registered as a short code, toll-free or 10DLC?
  • Area code match – does the sender/recipient area code match?
  • Opt-out rate – what is the sending number’s opt-out rate?
  • Sending Volume – what is the average sending volume?
  • Reply/engagement rate – what is the positive reply rate (excluding opt-outs) of the messages sent?
  • Not-deliverable – how many messages are non-deliverable (invalid numbers, land lines, etc.)?
  • Content filtering – has the content been filtered for S.H.A.F.T. content or other violations?
  • Embedded URLs – are the embedded URLs using public URL shorteners?
  • Content at URL – what type of content is hosted at the URL?
  • Embedded number – is a number embedded in the message that is different than the sending number?
  • Image content – was filtered content found through optical character recognition of an image?

The carriers do not publish how they evaluate sending number reputation. These are factors learned and shared within the industry.

What happens when you don’t properly warm-up a sending number?

When you don’t properly warm up your sending number you put yourself at risk for a high number of carrier violations and impacting future delivery.

Before you start the SMS number warm-up

Before you start your SMS number warm-up, we recommend following the steps in this checklist.

Consider the type of number used for sending

The type of number used for sending impacts how you need to approach warming up your SMS number. An unregistered long code is the most difficult type of number to warm-up.

Sending number warm-up is most critical for unregistered long codes.

Perform a validation on your SMS sending list

A sending list validation is the process of taking your numbers and validating the type of number, the carrier and determining if the number is mobile capable.

We recommend validating a list if you haven’t sent a message in the past 30 days.

If you need assistance validating your SMS sending list, please contact us as we can help.

Perform continuous validation

Ideally for every new mobile number added it should be validated to ensure it is a valid mobile number capable of receiving SMS messages.

Segment your list

Segmentation is the process of grouping your contacts by common characteristics. When it comes to warming up your sending number use segmentation to create smaller audiences that you can use in the warm-up sequence:

  • Segment by carrier – Create segments based on the carrier you are sending to.
  • Segment by engagement – If you are bringing an existing list, who are your most engaged vs. least engaged numbers.
  • Segment by region – Especially if you are retail location. You will only want to target recipients in your geographical area.
  • Segment by acquisition – How and where did you acquire the numbers? Did they sign up in  your store, on your website or through a QR code?
  • Segment by opt-in status – It’s critical that when you bring numbers into your sending list that you include numbers that have opted out. Versus just deleting those numbers. You want to bring those numbers with you to ensure they cannot get accidentally added back to a list.

For SMS warm-up we recommend trying to create segments with no more than 1,000 recipients.

Avoid common blocklist words

We’ve put together a list of common block words that can cause problems for your email marketing and SMS marketing. Get the full list as a Google Sheet or fork it from GitHub.

Block list management is built-in to DailyStory’s SMS delivery score.

Sender number planning

Depending upon the type of sending number you are using, you may need to consider using multiple sending numbers. This typically applies to 10 digit long codes.

Each sending number is assigned a through-put that each carrier will allow. This is the maximum number of messages per minute/hour/day they will allow you to send.

Exceeding your sending number through-put will cause carrier violations and prevent message delivery.

How many sending numbers do I need?

The general guidance for 10 digit long codes is approximately 1 number for every 1,000 recipients sent in a 1 hour time window. This also assumes no message variability, i.e. the same message to 1,000 recipients. And, ideally, you have multiple sending numbers to match recipients area codes.

Don’t approach your SMS strategy as “text blasting”

Unfortunately text message blasts and text message blast services are no longer as effective as they once were. This is due to changing consumer acceptance of text message marketing as well as changes in carrier regulations around customer communication.

Avoid services that advertise as a text blasting service or mass texting services. Using these types of service will only cause damage to you brand’s reputation.

Unless you are using a short code for sending your text messages, you can no longer send high volume text messages.

Utilize cross-channel for SMS marketing

SMS marketing should be one of many digital marketing channels you are using. And, ideally, email marketing and social media marketing are both in use as well.

Below are some ideas for how you can reenforce your SMS marketing through other channels:

  • Include sign up offers – within you email marketing, include offers exclusively available through SMS. For example, “text JOIN to 555-XXX-XXXX to get a 15% coupon for Cyber Monday.”
  • Display QR codes – if you are a retail location, take advantage of QR code that can be “scanned to sign up”. Scanning the QR code creates the text message to your number and all they have to do is click send.
  • Include website promotions – use popups and banners to encourage visitors to sign up for your deals and offers. Not just for your newsletter.
  • Reference in social media – reference your SMS marketing in social media posts as another way to access deals and offers.

Promote your SMS marketing through other digital marketing channels.

Something we often recommend is pairing your SMS marketing sends with your email marketing sends. For example, in your email marketing campaign reference, “be on the lookout for a text message from us”.

Update your website’s terms of service

A best practice is to include details about your SMS marketing in your website’s terms of service. We’ve put together a sample terms of service you can start with.

SMS marketing content planning

The most difficult part of creating a successful SMS marketing strategy is content planning and creation.

It’s important to resist the urge to send text blasts. Instead you will need to create a content strategy for your SMS marketing that follows best practices and matches the customers where they are in their journey with your brand.

Unique message content

We recommend creating a unique message per-500 recipients. And, the more unique messages you create the better.

We recommend one unique message per-500 recipients.

A unique message does not include simple applications of personalization.

Leverage writing assistant tools like ChatGPT

Using AI to help you write content is a great way to use modern tools like ChatGPT.

A ChatGPT writing assistant is built-in to DailyStory.

You can take a single SMS message and ask the writing assistant to create variations. Make the variations more sales-focused, less sales-focused and so on. Experiment with multiple versions of your message and then use tools like A/B testing to test different messages.

Targeted, journey-specific messaging

Your text message recipients will be at different places in their journey with your brand. Using the four stages of the marketing funnel is a simple way to break this down:


When building your SMS marketing content for customers at the awareness stage:

  • Confirm sign-up intent – use tools like double opt-in to confirm the intent to sign up. Especially if they signed up on your website without texting in a sign-up keyword.
  • Reenforce brand – throughout all the messaging during the awareness phase, you want to ensure the recipient is aware of who the brand is and what number they will receive messages from.
  • Encourage replies – seek to create content that is establishing a rapport with the customer with two-way communication. Even if responses to that communication is automated.
  • Limit sales messaging – only one out of every three messages should be sales oriented. Your goal here is to establish a pattern with the carriers that shows positive intent between the sending number and the recipient.

Text messages in this stage should not include URLs. We recommend not including URLs in  your text messages until you’ve moved deep into the consideration phase or are well into the conversion phase.

In this stage we like to use keyword automations, drip campaigns and other non-marketing style messages to warm the audience up to your send frequency.


Once a customers is successfully transitioned through the awareness stage, whose primary purpose is to establish brand identity and trust of the sending number, now you can start marketing and selling.

  • Establish a cadence – is your messaging sending once a week or once a month? In our experience, once a month is frequent enough to keep a buyer engaged.
  • Remain conversational, but introduce promotions – it’s still important that the messaging is bi-directional. But, you can begin to introduce more promotion content.

The goal in the stage is to motivate your prospect to do something. This something can be click a link, reply with a keyword, make a purchase or perform another transaction with your business.

Including URLs in your text message can be done here once you’ve established your sending number with the recipient. But you should still be cautious as URLs can cause delivery issues.


You’ve successfully acquired a prospect. You’ve navigated them through the awareness and consideration phase and slowly introduce sales-specific messaging.

They have now converted, whether in-store or online.

  • Understand the type of customer – is your store a physical retail location? Is your customer geographically “close” to your location? If not, this is probably not someone that you want to message frequently.

For customers outside your geographic target range, reduce the messaging frequency to correspond with season activity, e.g. summer, labor day, Christmas, or other times when these customers may be “visiting” the location.

  • Post-purchase follow-up – now is a great time to run post-purchase follow-up campaigns. Still with an emphasis on your brand recognition.
  • Surveys – a SMS-based survey, e.g. reply 5 if you had an excellent experience to 1 if you had a poor experience, is a great way to engage your customers in conversational messaging.


Once you’ve converted a customer your marketing campaign changes to focus on loyalty and cross- selling.

  • Introduce complimentary products – find the products that compliment other purchases the customer has made and use this as a cross-sell opportunity.
  • Introduce rewards – celebrate customer purchasing levels with rewards offered for achieving different milestones, e.g. $100 spent, $500 spent and so on.
  • Celebrate together – celebrate customer anniversaries, purchasing milestones through loyalty. These are great ways to keep customers engaged with your brand.
  • Ask for reviews – use your SMS marketing channel to ask customers to leave reviews for you on important pages like Google My Business.

Every 3rd message should encourage a reply

Resist the temptation to focus exclusively on outbound marketing and sales messages.

Unfortunately most brands want to focus exclusively on outbound without investing on inbound. Inbound replies help build your sending reputation.

In our experience with long code and toll-free sending numbers, it is best to ensure that at least one out of every three messages encourages a reply.

Examples of messages that encourage replies:

  • Inquire about recent experience – what was their favorite product or experience.
  • Ask about what they are looking forward to – especially as it relates to new products.
  • Ask about favorite brands – what are their favorite brands they have purchased.
  • Surveys – ask for feedback on a recent store visit.
  • Question based messages – examples, “we’re hosting an event Saturday night. Will you be there?”.

The goal is to encourage replies. When the carriers see replies to your messages these are positives signals about your sending number reputation.

Remember, opt-out messages are negative signals

Imagine from the other perspective where all a brands sends is sales and promotional materials. The only replies received back are optouts: STOP, QUIT, UNSUBSCRIBE, etc.

Opt-out messages are huge negative signals.

Non-opt-opt out messages are positive signals whereas negative and optout messages are negative signals about your numbers sending reputation.

Recommend Best Practices for SMS warm-up

Below are some recommended best practices for warming up a new sending number.

  • Start slow, then go even slower – if you are attempting to send more than 500 messages in a single send, it’s best to drip them out slowly. Eventually you’ll send at a higher throughput, but you have to start slow.
  • Watch the undeliverable messages – a sudden spike in opt-outs or undeliverable messages is an indicator that you need to slow down.
  • Randomize the send time – don’t send all your messages at the same time. View this instead of how many messages you are sending to each carrier.
  • Start with your most engaged recipients – start with the recipients that are most engaged or have most recently been sent messages.

Encourage replies to your messages

We’ve repeated this multiple times in this article, but it can’t be stated enough: replies are a positive signal.

An example warm-up schedule

Putting together a plan for how you warm-up your sending numbers is important. And, it depends on whether you are trying to warm up a number you have not previously used or if you are moving your SMS marketing list to a new platform.

The warm-up schedule below is an example of how you would warm-up a list of 10,000 numbers sending from new sending numbers. It assumes that the customer has not received an text message from this number previously:

Preparation – list clean up and planning

The very first thing to do is to run your list of 10,000 numbers through a list clean up. This is something DailyStory can help with. Next, create segments for the major providers: AT&T, Verizon and T-Mobile. Finally, create segments for your different audiences.

We’ve covered this extensively in the above sections.

Days 1 – 30 – start the sending

Send to 300-500 unique recipients per-day.

  • If you delivery rate is low due to sending errors, such as carrier violations, slow down.
  • If you see an opt-out rate greater than 1%, slow down the sending even further until the opt-out rate is below 1% consistently.
  • Focus on messages that are conversational and are reintroducing your brand.

Ideally, during this phase you are sending to contacts that are engaged and expect your messages.

If you see any issues with deliverability or high opt outs, slow down the send rate.

Days 30 – 60 – increase the volume

At this point everyone on your list has received at least one text messages, but possibly more. You can now slowly start working up the volume of sends.

The rules laid out in days 1-30 still apply. If you start seeing any delivery issues, slow down the sending.

Common mistakes

Below are some common mistakes to avoid when warming up an SMS sending number.

Poor brand recognition

This is especially true if you haven’t sent a text message in more than 30 days or if this is the first text message you are sending.

Use an MMS (multimedia text message) with your brand’s logo to help reinforce the identity of the sending number.

  • Example MMS

  • Hi it’s Anna from DailyStory
    I wanted to follow up on your recent purchase. Do you have some time to talk?
    Reply STOP to opt out.

MMS messages are more expensive. So if you don’t want to use an MMS make sure and include brand information the text of your message.

  • Example SMS
  • Hi it’s Anna from DailyStory
    I wanted to follow up on your recent purchase. Do you have some time to talk?
    Reply STOP to opt out.

High frequency sending number rotation

While not applicable to registered sending numbers, sending number rotation – known as snowshoeing – is highly discouraged. Not only does this cause confusion for your customers, as they will receive messages from a number they previously have never received from, but it requires a full warm-up of your sending number.

Avoid releasing and leasing new sending numbers. As you will need to go through the entire warm-up sequence again.

Sending to non-engaged or opted out contacts

Unfortunately one of the the most common mistakes is attempting to reactivate opted-out contacts. It’s important that when you bring data from one platform to another that you bring this data with you, but that it is brought-in as opted out.

Routinely remove unengaged numbers from your list.

Similarly, you should routinely pare down your sending lists and remove unengaged contacts. These are contacts that have not replied, clicked or perhaps even purchased recently.

Too aggressive send rates

The next most common mistake is sending too many text messages too quickly. Known as text blasting, this type of messaging strategy is ineffective and will only cause carrier violations.

What about shared short codes?

At one point carriers allowed senders to use shared short codes. This was the practice of a short code owner allowing multiple brands to send text messages using that short code. This is no longer allowed.

What about ported numbers?

When you port a number you move your sending number from one provider to another. For example, moving a number from Twilio to Sinch.

In our experience, when a number is ported from one provider to another the reputation of the number is carried with the port.

Ported numbers can be considered warm.

However, just because the ported number is considered warm you should ensure that your audience engagement.

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