SMS Senders

A sender ID is an originating phone number or string identifier used to indicate who an SMS message comes from. Members of your audience subscribe (opt in) to each sender ID they want to receive messages from.

Sender types

There are various types of SMS senders, each with their own advantages and disadvantages.

Primary differences between sender types:

Sender typeDescriptionExampleCommunicationBest useProvisioning time
Short code (Dedicated or Shared)Numeric, 3-8 digits, typically 5-6 digits56582Two-way1Notifications, alerts, marketingDedicated: Weeks to months
Shared: Days to weeks
Long codeNumeric, a standard phone number, 10 digits in most countries15556059987Two-way and voiceCommunication with one recipient at a timeHours to weeks
Alphanumeric codeAlphanumeric, 2-11 characters and can include spaces, also known as an “alpha” codeAIRSHIP, BrandName, PSA123One-wayNotifications, alerts, marketingDays to weeks

1. Support for two-way communication varies by country.

Short codes

Short codes have several advantages that make them the superior sender type, including:

  • Designed to send high volumes of messages at high throughput
  • Short in length, making them easy for consumers to recall
  • Capable of two-way messaging, so you can effectively manage opt-in and compliance workflows with keyword responses

However, they are the most expensive sender type and can take months to provision.

There are two short code types: dedicated and shared. In 2021, US mobile carriers discontinued approval for new shared short codes. Airship does not support shared short codes for outbound messaging.

Primary differences between short code types:

Dedicated short codeShared short code
OperationUsed by a single brand to communicate with consumersUsed by multiple brands to communicate with consumbers, where permitted
Region supportAvailable in all countries with SMS serviceNot approved for use in all countries with SMS service
LeaseMust be leased from a service provider for a period of three, six, or 12 monthsNo lease requirement, but Airship may or may not have a shared short code available in your desired country
Provisioning timeWeeks to monthsDays to weeks

Long codes

Long code advantages:

  • Less expensive and shorter provisioning time than short codes
  • Support both voice and text
  • May be recognizable to consumers if otherwise associated with your business
  • Capable of two-way messaging, so you can effectively manage opt-in and compliance workflows with keyword responses

They are generally used for lower volume, transactional messaging and at lower throughput than short codes or alpha codes.

Primary differences between long code types:

Virtual number10-digit long code (10DLC)Toll-free number (TFN)
FormatInternational standard or local numberUS or CA standard or local numberBusiness number beginning with a recognizable prefix: 800, 888, 877, 866, 855, 844, or 833
Region supportAvailable in most countries with SMS serviceAvailable in US and CanadaAvailable in US and Canada
TrafficReserved for person-to-person (P2P) traffic, can be used for limited application-to-person (A2P) interactionsReserved for A2P trafficReserved for A2P traffic
ThroughputLow: 1 MPSVaries by carrier, use case and brand score, starts at 1 MPSVaries by use case, starts at 10 MPS
Daily message limitVaries by countryVaries by carrierVaries by carrier
Provisioning timeDaysDays to weeks, requires campaign registrationHours to days, requires sender verification

Alpha codes

Alpha codes have become a common sender type for SMS marketers throughout the world, largely because of their advantages:

  • Can be a brand name or other recognizable term
  • Shorter provisioning time than short codes
  • Lower in cost than dedicated short codes since they don’t require leasing and may not require registration
  • Capable of high volume messaging

However, they are a one-way sender, so cannot receive inbound SMS (mobile originating, or MO) messages. This can be a problem for brands required to maintain regulatory compliance with SMS keywords. The next section explains how to maintain keyword compliance when using alpha senders.

Message forwarding

Brands may be required use a two-way sender in order to receive inbound (MO) messages so they can maintain regulatory compliance with SMS keywords. Maintaining compliance is not possible when using only a one-way sender, for example an alpha sender.

The main compliance concerns are opting users out of commercial messaging and providing a way to contact the sender for more information. Example keywords for compliance: STOP, HELP, CONTACT.

You can maintain compliance by forwarding messages from a two-way sender to an alpha sender.

  • Inbound message handling — Inbound messages (MO) are forwarded to whichever associated alpha sender sent the last outbound (MO) message to the corresponding MSISDN within the last 72 hours.

    If an alpha sender has not sent an outbound (MT) message to a MSISDN within the last 72 hours, the inbound (MO) message will not be forwarded, and the subscriber will receive a generic response telling them that their request cannot be processed.

  • Multiple alpha senders — You can use a single forwarding sender for multiple alpha senders. Inbound message forward to the alpha sender that last sent an outbound (mobile terminated, or MT) message to the recipient MSISDNThe mobile phone number of an individual in your Airship audience. Each MSISDN represents an individual mobile device. . This behavior is significant when using the same forwarding sender for multiple projects or using a shared short code as a forwarding sender.

  • Keyword responses and actions — The alpha sender handles all keyword processing of requests and actions, such as triggering a text response, opting in a user, or applying a tag for segmentation. Keyword responses are also sent from the alpha sender, as if it had received the inbound (MO) message without forwarding. See SMS Keywords.

Any sender capable of receiving inbound (MO) messages can be configured as a forwarding sender. Forwarding senders operate in the same country of origin as the alpha sender.

See also SMS Compliance.

Setting up message forwarding

Airship configures forwarding senders for your project, however the forwarding sender cannot be configured to handle any keywords. Remove keywords for that sender before making your request. See SMS Keywords.

Contact Support or your account manager with your request and include these identifiers:

IdentifierDescriptionWhere to find it in your Airship project
Project app keyThe identifier for the project you want enabled for forwarding SMS messagesGo to Settings and copy the app key from the sidebar.
Forwarding senderThe sender ID for the two-way sender that should forward messages to your alpha codeSee instructions that follow this table. If you do not have a two-way sender to use as your forwarding sender, instead request that Airship provision one for you.
Alpha senderThe sender ID for the alpha code that should receive the forwarded messagesSee instructions that follow this table. If you do not have an alpha code, instead request that Airship provision one for you.

If you do not know what senders are already configured for your project, you can find them in the Airship dashboard:

  1. Go to Messages, then SMS Keywords.
  2. Select   Create new keyword.
  3. Select Settings, then the SMS Sender menu. You will see all the long codes and short codes for your project. Each sender in the list is formatted as a 2-character country code followed by the actual long or short code.
  4. Note the long and short codes, then leave the page without saving a new keyword.

If you need forwarding senders for multiple projects, you may want to make a separate request per project for easier tracking.


Support or your account manager will tell you when configuration is complete and you can start including the forwarding sender ID in your SMS messages.

Setting up keywords

Outbound messages should include instructions explaining how your SMS subscribers can respond. For example, you might include Text STOP to <forwarding sender ID> to opt out. See SMS Keywords to set up keywords for your alpha sender.