Hello this is SureM.

Sometimes although the messages is "Delivered", end user still unable to receive the messages.

This is because the end user registered for SPAM Blacklist to KISA in South Korea.

Spam filtering and spam blocking (SKT, KT, LG U+) are automatically subscribed to all customers of mobile carriers.

Each carrier has different types of spam blocking settings, so even its the same carrier, the type of recipient's settings will depend on whether or not to receive the text box.

Therefore, end recipient must check:

1) SPAM box

2) Operator spam application

For inquiry please send to intlsales@surem.com