How can I prevent my messages from being filtered as spam?

Carriers have an obligation to their users to combat spam. Part of the way that carriers combat spam is by “filtering” messages wich are suspected of being spam. When a message is “filtered”, it will not be delivered to the end user, and no notice will be given to the sending party that anything out of the ordinary has taken place. After all, if carriers told spammers when they had detected spam, spammers would quickly change their sending patterns and start sending spam again.

Very rarely, when several messages that match the carrier’s criteria for being spam are detected coming from a number, the carrier will block the delivery of subsequent messages from that number to their network.

These sorts of problems are rarely encountered, and are easy to avoid by following some simple best practices:

  • Use a short code if you plan to send marketing messages.
  • Only ever send SMS messages to people who expect and appreciate them. Carriers are quick to block numbers when they receive subscriber complaints. Provide customers with a way to contact you directly so they don’t need to complain to their carrier.
  • Try not to send more than 5 messages per minute from a single number. If you need to learn how to slow down the rate at which you are sending your messages, check out this blog post on message scheduling.
  • Distribute your traffic across a few numbers, if necessary.
  • Avoid sending perfectly identical messages. These may look to carriers like spam.
  • Be careful what links you are sending. Some services (like fb.me, goo.gl and tinyurl) have been blocked by certain carriers in some countries because of prior abuse by spammers. Test to make sure that the links you are including aren’t causing your messages to be blocked on your target carriers before you send a lot of messages.
  • Occasionally test your number to ensure that messages are still being delivered as expected.