The Japanese government is cracking down on mobile phone spam.
According to the Daily Yomiuri newspaper, more than 950 million emails are sent and received on mobiles every day with more than 84 per cent of them - about 800 million messages - consisting of spam.
This week the Japanese government passed new legislation which will force spammers to put a special identifying character in the subject line of each ad message.
And NTT DoCoMo says that it will allow users to block all mails bearing the asterisk-like symbol from October.
The new law requires commercial messages to include the full name, address and email address of senders. It also allows recipients to opt-out of further messages from the same source.
If the spammers fail to comply with the rules they could be fined more than £2,700.