- Poor or low coverage
- The receiving mobile phone was switched off for more than 2 days
- SMS barring is activated
- Call barring of incoming calls is activated
- Inbox is full
- Sender’s mobile number is in recipient’s “Block List”
- Phone is out of coverage
- SMS will be sent once phone is switched on
- If maximum capacity of sever is reached before phone is switched on, SMS will be erased
